## Description

**INSTANT DOWNLOAD COMPLETE TEST BANK WITH ANSWERS**

###### College Physics A Strategic Approach 2nd Edition by Knight – Test Bank

*College Physics, 2e*** (Knight)**

**Chapter 2 Motion in One Dimension**

** **

**2.1 Quantitative**

** **

1) A car accelerates from 5.0 m/s to 21 m/s at a rate of 3.0 m/s2. How far does it travel while accelerating?

- A) 69 m
- B) 207 m
- C) 41 m
- D) 117 m

Answer: A

Var: 50+

2) An airplane needs to reach a velocity of 203.0 km/h to take off. On a 2000 m runway, what is the minimum acceleration necessary for the plane to take flight?

- A) 0.79 m/s2
- B) 0.87 m/s2
- C) 0.95 m/s2
- D) 1.0 m/s2

Answer: A

Var: 50+

3) Assuming equal rates of acceleration in both cases, how much further would you travel if braking from 56 mi/h to rest than from 28 mi/h?

- A) 4 times farther
- B) 3.2 times farther
- C) 4.8 times farther
- D) 5.2 times farther

Answer: A

Var: 50+

4) A 8.7 hour trip is made at an average speed of 73.0 km/hr. If the first third of the trip (chronologically) was driven at 96.5 km/hr, what was the average speed for the rest of the journey?

- A) 61 km/hr
- B) 51 km/hr
- C) 67 km/hr
- D) 85 km/hr

Answer: A

Var: 50+

5) If the fastest you can safely drive is 65 mi/h, what is the longest time you can stop for dinner if you must travel 541 mi in 9.6 h total?

- A) 1.3 h
- B) 1.4 h
- C) 1.0 h
- D) You can’t stop at all.

Answer: A

Var: 50+

6) A car travels 95 km to the north at 70.0 km/h, then turns around and travels 21.9 km at 80.0 km/h. What is the difference between the average speed and the average velocity on this trip?

- A) 27 km/h
- B) 19 km/h
- C) 32 km/h
- D) 24 km/h

Answer: A

Var: 50+

7) A baseball is hit with a bat and, as a result, its direction is completely reversed and its speed is doubled. If the actual contact with the bat lasts 0.45 s, what is the ratio of the acceleration to the original velocity?

- A) -6.7 s-1
- B) -4.4 s-1
- C) -2.2 s-1
- D) -0.15 s-1

Answer: A

Var: 50+

8) A sports car has an average acceleration of 13.1 . How long does it take for the car to reach 60.0 mi/h, if it starts from rest?

- A) 4.6 s
- B) 5.5 s
- C) 3.1 s
- D) 8.8 s

Answer: A

Var: 50+

9) A car is travelling north at 17.7 m/s. After 12 s its velocity is 14.1 m/s in the same direction. Find the magnitude and direction of the car’s average acceleration.

- A) 0.30 m/s2, South
- B) 2.7 m/s2, South
- C) 0.30 m/s2, North
- D) 2.7 m/s2, North

Answer: A

Var: 50+

10) Acceleration is sometimes expressed in multiples of g, where g = 9.8 m/s2 is the acceleration due to the earth’s gravity. In a car crash, the car’s velocity may go from 26 m/s to 0 m/s in 0.15 s. How many g’s are experienced, on average, by the driver?

- A) 18 g
- B) 13 g
- C) 22 g
- D) 23 g

Answer: A

Var: 11

11) A train starts from rest and accelerates uniformly, until it has traveled 5.6 km and acquired a velocity of 42 m/s. The train then moves at a constant velocity of 42 m/s for 420 s. The train then slows down uniformly at 0.065 m/s2, until it is brought to a halt. The acceleration during the first 5.6 km of travel is closest to:

- A) 0.16 m/s2
- B) 0.14 m/s2
- C) 0.17 m/s2
- D) 0.19 m/s2
- E) 0.20 m/s2

Answer: A

Var: 50+

12) A train starts from rest and accelerates uniformly, until it has traveled 2.1 km and acquired a velocity of 24 m/s. The train then moves at a constant velocity of 24 m/s for 400 s. The train then slows down uniformly at 0.065 m/s2, until it is brought to a halt. The distance traveled by the train while slowing down, in km, is closest to:

- A) 4.4
- B) 4.2
- C) 4.0
- D) 3.8
- E) 3.6

Answer: A

Var: 50+

13) A car moving at a velocity of 20 m/s is behind a truck moving at a constant velocity of 18 m/s. When the car is 50 m behind the front of the truck, the car accelerates uniformly at 1.8 m/s2. The car continues at the same acceleration until it reaches a velocity of 25 m/s, which is the legal speed limit. The car then continues at a constant velocity of 25 m/s, until it passes the front of the truck. The distance the car travels while accelerating, in meters, is closest to:

- A) 50
- B) 54
- C) 58
- D) 62
- E) 66

Answer: D

Var: 1

14) A motorist makes a trip of 180 miles. For the first 90 miles she drives at a constant speed of 30 mph. At what constant speed must she drive the remaining distance if her average speed for the total trip is to be 40 mph?

- A) 45 mph
- B) 50 mph
- C) 52.5 mph
- D) 55 mph
- E) 60 mph

Answer: E

Var: 1

15) A dragster travels 1/4 mi in 6.7 s. Assuming that acceleration is constant and the dragster is initially at rest, what is its velocity when it crosses the finish line?

- A) 269 mi/h
- B) 188 mi/h
- C) 296 mi/h
- D) 135 mi/h

Answer: A

Var: 40

16) The average velocity of a car over a certain time interval is 37 mi/h. If the velocity of the car was 65 mi/h at the end of this interval, what was its initial velocity? Assume that acceleration was constant.

- A) 9 mi/h
- B) 13 mi/h
- C) 4.0 mi/h
- D) 57 mi/h

Answer: A

Var: 25

17) A racquetball strikes a wall with a speed of 30 m/s and rebounds with a speed of 26 m/s. The collision takes 20 ms. What is the average acceleration of the ball during the collision?

- A) zero
- B) 200 m/s2
- C) 2800 m/s2
- D) 1500 m/s2
- E) 1300 m/s2

Answer: C

Var: 1

18) Human reaction times are worsened by alcohol. How much farther would a drunk driver’s car travel before he hits the brakes than a sober driver’s car? Assume both cars are initially traveling at 49.0 mi/h, the sober driver takes .33 s, and the drunk driver takes 1.0 s to hit the brakes in a crisis.

- A) 48 ft
- B) 34 ft
- C) 53 ft
- D) 58 ft

Answer: A

Var: 30

19) A bicyclist starts a timed race at 6.0 mi/h. In order to win, he must average 21 mi/h. Assuming constant acceleration from the start, how fast must he be traveling at the end of the race?

- A) 36 mi/h
- B) 30 mi/h
- C) 24 mi/h
- D) 42 mi/h

Answer: A

Var: 21

20) A toy rocket is launched vertically from ground level (y = 0 m), at time t = 0.0 s. The rocket engine provides constant upward acceleration during the burn phase. At the instant of engine burnout, the rocket has risen to 64 m and acquired a velocity of 60 m/s. The rocket continues to rise in unpowered flight, reaches maximum height, and falls back to the ground. The time interval, during which the rocket engine provides upward acceleration, is closest to:

- A) 2.1 s
- B) 2.3 s
- C) 1.9 s
- D) 1.7 s
- E) 1.5 s

Answer: A

Var: 50+

21) A toy rocket is launched vertically from ground level (y = 0 m), at time t = 0.0 s. The rocket engine provides constant upward acceleration during the burn phase. At the instant of engine burnout, the rocket has risen to 81 m and acquired a velocity of 40 m/s. The rocket continues to rise in unpowered flight, reaches maximum height, and falls back to the ground. The upward acceleration of the rocket during the burn phase is closest to:

- A) 9.9 m/s2
- B) 9.6 m/s2
- C) 9.3 m/s2
- D) 9.0 m/s2
- E) 8.7 m/s2

Answer: A

Var: 50+

22) A toy rocket is launched vertically from ground level (y = 0 m), at time t = 0.0 s. The rocket engine provides constant upward acceleration during the burn phase. At the instant of engine burnout, the rocket has risen to 49 m and acquired a velocity of 60 m/s. The rocket continues to rise in unpowered flight, reaches maximum height, and falls back to the ground. The maximum height reached by the rocket is closest to:

- A) 233 m
- B) 221 m
- C) 209 m
- D) 244 m
- E) 256 m

Answer: A

Var: 50+

23) A ball is thrown straight upward with a velocity of 39 m/s. How much time passes before the ball strikes the ground? (Disregard air resistance.)

- A) 8.0 s
- B) 4.0 s
- C) 2.4 s
- D) 1.2 s

Answer: A

Var: 31

24) A package is dropped from a helicopter moving upward at 15 m/s. If it takes 16.0 s before the package strikes the ground, how high above the ground was the package when it was released? (Disregard air resistance.)

- A) 1000 m
- B) 1500 m
- C) 810 m
- D) 1200 m

Answer: A

Var: 25

25) At the same moment, one rock is dropped and one is thrown downward with an initial velocity of 10 m/s from the top of a 300 m building. How much earlier does the thrown rock strike the ground? (Disregard air resistance.)

- A) 0.95 s
- B) 0.66 s
- C) 0.85 s
- D) They land at exactly the same time.

Answer: A

Var: 21

26) A ball is projected upward at time t = 0.0 s, from a point on a roof 60 m above the ground. The ball rises, then falls and strikes the ground. The initial velocity of the ball is 28.4 m/s. Consider all quantities as positive in the upward direction. At time t = 4.3 s, the acceleration of the ball is closest to:

- A) zero
- B) +5 m/s2
- C) +10 m/s2
- D) -5 m/s2
- E) -10 m/s2

Answer: E

Var: 50+

27) A ball is projected upward at time t = 0.0 s, from a point on a roof 90 m above the ground. The ball rises, then falls and strikes the ground. The initial velocity of the ball is 80.5 m/s. Consider all quantities as positive in the upward direction. The velocity of the ball when it is 89 m above the ground is closest to:

- A) – 81 m/s
- B) – 64 m/s
- C) – 48 m/s
- D) – 32 m/s
- E) – 97 m/s

Answer: A

Var: 50+

28) A test rocket is fired straight up from rest with a net acceleration of 20 m/s2. After 4 seconds the motor turns off, but the rocket continues to coast upward. What maximum elevation does the rocket reach?

- A) 487 m
- B) 327 m
- C) 320 m
- D) 408 m
- E) 160 m

Answer: A

Var: 1

29) A sports car can go from rest to 32 m/s in 3.88 s. The same car can come to a full stop from that speed in 3.96 s. What is the ratio of starting to stopping accelerations?

- A) -1.0
- B) 1.0
- C) -0.98
- D) 0.98

Answer: A

Var: 50+

**2.2 True/False**

** **

1) The acceleration is always the slope of the “velocity versus time” graph and the velocity is always the slope of the “position versus time” graph.

Answer: TRUE

Var: 1

2) It is not physically possible for the “position versus time” graph of a moving animal to be either perfectly vertical or perfectly horizontal.

Answer: TRUE

Var: 1

3) The equation sf = si + vis Δt + as (Δt)2 is valid for all types of motion because it is a fundamental equation of physics.

Answer: FALSE

Var: 1

4) Negative acceleration is called deceleration because an object is slowing down.

Answer: FALSE

Var: 1

5) The equation vfs2 = vis2+ 2as Δx applies to motion for which the “velocity versus time” graph is a straight line.

Answer: TRUE

Var: 1

6) If an object stops moving at a point, then its acceleration must be zero at that point.

Answer: FALSE

Var: 1

7) It is physically impossible for an object to have a negative acceleration and yet be speeding up.

Answer: FALSE

Var: 1

8) If the “velocity versus time” graph of an object is a horizontal line, that object cannot be accelerating.

Answer: TRUE

Var: 1

**2.3 Conceptual**

** **

1) What quantity is measured by your speedometer (be as specific as possible)?

Answer: Your speedometer tells you the __instantaneous__ speed of your car.

Var: 1

2) You go on a long trip and try to determine your average velocity by using the miles on your car’s tripometer and the time the trip required. Why would the answer using this information most likely __not__ be correct?

Answer: Unless the trip was along a perfect straight line, the distance on the tripometer would __not__ be your displacement. The quantity calculated would thus be your average speed, not your average velocity.

Var: 1

3) Is there any situation in which the average velocity of an object can be greater than the object’s average speed? Support your answer.

Answer: The average velocity can never be greater than the average speed. The two averages will be equal for motion along a single straight path; otherwise the average speed is always greater.

Var: 1

4) It is possible to have a negative average velocity, depending on the choice of coordinate system. Is it possible for an object to have a negative average speed?

Answer: No. An object’s average speed must always be greater than or equal to zero, regardless of coordinate system.

Var: 1

5) A skier begins skiing straight down a hill having a constant slope, starting from rest. If friction is negligible, as the skier goes down the hill, his/her

- A) acceleration is constant, with a value less than 10 m/s/s.
- B) acceleration is constant, with a value of roughly 10 m/s/s.
- C) acceleration increases with time.
- D) acceleration is zero.

Answer: A

Var: 1

6) A person in a car is driving down a straight road. The instantaneous acceleration is decreasing with time, but is directed in the direction of the car’s motion. The speed of the car is

- A) increasing with time.
- B) decreasing with time.
- C) constant.

Answer: A

Var: 1

7) A child standing on a bridge throws a rock straight down. The rock leaves the child’s hand at

t = 0. Which of the graphs shown here best represents the velocity of the stone as a function of time?

- A)
- B)
- C)
- D)
- E)

Answer: C

Var: 1

8) The plot below shows the position of an object as a function of time. The letters H-L represent particular moments of time. At which moment in time is the speed of the object the highest?

- A) J
- B) H
- C) I
- D) K
- E) L

Answer: A

Var: 1

9) The plot below shows the position of an object as a function of time. The letters H-L represent particular moments of time. At which moment in time is the speed of the object equal to zero?

- A) I
- B) H
- C) J
- D) K
- E) L

Answer: A

Var: 1

10) The motions of a car and a truck along a straight road are represented by the velocity-time graphs below. The two vehicles are initially alongside each other at time t = 0.

At time T, what is true of the distances traveled by the vehicles since time t = 0?

- A) They will have traveled the same distance.
- B) The truck will not have moved.
- C) The car will have traveled farther than the truck.
- D) The truck will have traveled farther than the car.

Answer: D

Var: 1

11) Two identical objects A and B fall from rest from different heights to the ground. If object B takes *twice* as long as A to reach the ground, what is the ratio of the heights from which A and B fell? Neglect air resistance.

- A) 1 :
- B) 1 : 2
- C) 1 : 4
- D) 1 : 8

Answer: C

Var: 1

12) A ball is thrown vertically upward and then comes back down. During the ball’s flight up and down, its **velocity** and **acceleration** vectors are

- A) always in opposite directions.
- B) always in the same direction.
- C) first in opposite directions and then in the same direction.
- D) first in the same direction and then in opposite directions.

Answer: C

Var: 1

13) A racing car accelerates uniformly from rest along a straight track. This track has markers spaced at equal distances along it from the start, as shown below. The car reaches a speed of 140 km/h as it passes marker 2.

Whereabouts on the track was the car when it was travelling at half this speed, i.e. at 70 km/h?

- A) before marker 1
- B) at marker 1
- C) between marker 1 and marker 2

Answer: A

Var: 1

14) A stone is thrown vertically upwards, reaches a highest point, and returns to the ground. When the stone is at the **top** of its path, its acceleration

- A) is zero.
- B) is directed upwards.
- C) is directed downwards.
- D) changes direction from upwards to downwards.

Answer: C

Var: 1

15) Two identical stones are dropped from a tall building, *one after the other*. Assume air resistance is negligible. While both stones are falling, what will happen to the vertical distance between them?

- A) It will increase.
- B) It will decrease.
- C) It will remain the same.
- D) It will first increase and then remain constant.

Answer: A

Var: 1

16) An object is dropped from rest into a pit, and accelerates due to gravity at roughly 10 m/s2. It hits the ground in 5 seconds. A rock is then dropped from rest into a second pit, and hits the ground in 10 seconds. How much deeper is the second pit, compared to the first pit? Neglect air resistance.

- A) four times deeper
- B) two times deeper
- C) three times deeper
- D) five times deeper

Answer: A

Var: 1

17) Which of the following situations is impossible?

- A) An object has velocity directed east and acceleration directed west.
- B) An object has velocity directed east and acceleration directed east.
- C) An object has zero velocity but non-zero acceleration.
- D) An object has constant non-zero acceleration and changing velocity.
- E) An object has constant non-zero velocity and changing acceleration.

Answer: E

Var: 1

*College Physics, 2e*** (Knight)**

**Chapter 4 Forces and Newton’s Laws of Motion**

** **

**4.1 Quantitative**

** **

1) A 27 kg object is accelerated at a rate of 1.7 m/s2. What force does the object experience?

- A) 46 N
- B) 16 N
- C) 63 N
- D) 98 N

Answer: A

Var: 16

2) It takes 4500 N to accelerate a car at a rate of 3.42 m/s2. What is the mass of the car?

- A) 1310 kg
- B) 1700 kg
- C) 1510 kg
- D) 1040 kg

Answer: A

Var: 50+

3) A Ferrari accelerates from 0 to 100.0 km/h in 4.80 s. What force (in Newtons) does a passenger of mass 68.0 kg experience during acceleration?

- A) 394 N
- B) 82.0 N
- C) 342 N
- D) 311 N

Answer: A

Var: 50

4) A child pulls on a wagon handle at an angle 37° above the horizontal with a force of 45 N. If the wagon accelerates at 8.1 m/s2 horizontally, what is the mass of the wagon? Assume frictional forces are negligible.

- A) 4.4 kg
- B) 5.6 kg
- C) 3.1 kg
- D) 3.7 kg

Answer: A

Var: 42

5) A child on a sled starts from rest at the top of a 15.0° slope. If the trip to the bottom takes

15.2 s, how long is the slope? Assume that frictional forces may be neglected.

- A) 293 m
- B) 586 m
- C) 1130 m
- D) 147 m

Answer: A

Var: 50+

6) On its own, a tow truck has a maximum acceleration of 3.0 ms-2. What would be the maximum acceleration when the truck was towing a bus of twice its own mass?

- A) 2.5 ms-2
- B) 2.0 ms-2
- C) 1.5 ms-2
- D) 1.0 ms-2

Answer: D

Var: 1

7) A 1100 kg car traveling at 27 m/s starts to decelerate and comes to a complete stop in 578.0 m. What is the average braking force acting on the car?

- A) -690 N
- B) -550 N
- C) -410 N
- D) -340 N

Answer: A

Var: 50+

8) The engine of a 1250 kg car provides a forward directed force of 3651 N. If the car accelerates at a rate of 2.60 m/s2, what is the total resistive force (wind resistance, friction, etc.) acting on the car?

- A) 401 N
- B) 8600 N
- C) 2400 N
- D) 485 N

Answer: A

Var: 50+

9) Two children fighting over a toy pull on the toy in different directions. One child pulls to the north with a force of 5.3 N, and the other child pulls to the east with a force of 6.3 N. What is the magnitude of the net force on the toy?

- A) 8.2 N
- B) 12 N
- C) 1.0 N
- D) 9.3 N

Answer: A

Var: 36

10) Two forces act on a 55 kg object. One force has magnitude 65 N directed 59° clockwise from the positive x-axis, and the other has a magnitude 35 N at 32° clockwise from the positive y-axis. What is the magnitude of this object’s acceleration?

- A) 1.1 m/s2
- B) 1.3 m/s2
- C) 1.5 m/s2
- D) 1.7 m/s2

Answer: A

Var: 46

11) The figure shows an acceleration-versus-force graph for a 125 g object. What should be the value of the first tick-mark on the vertical scale?

- A) 4
- B) 8
- C) 0.00400
- D) 0.00800

Answer: A

Var: 12

12) The figure shows an object’s acceleration-versus-force graph. What is the object’s mass in grams?

- A) 2.5
- B) 1.6
- C) 630
- D) 400,000

Answer: A

Var: 8

13) The figure shows two forces acting on an object. They have magnitudes **F1** = 6.3 N and

**F2** = 2.1 N. What third force will cause the object to be in equilibrium?

- A) 6.6 N at 162° counterclockwise from
- B) 6.6 N at 108° counterclockwise from
- C) 4.2 N at 162° counterclockwise from
- D) 4.2 N at 108° counterclockwise from

Answer: A

Var: 24

14) The figure shows two forces acting on an object, with magnitudes **F1** = 78 N and **F2** = 26 N. What third force will cause the object to be in equilibrium?

- A) 52 N pointing down
- B) 52 N pointing up
- C) 82 N pointing down
- D) 82 N pointing up

Answer: A

Var: 23

15) The figure shows an acceleration-versus-force graph for three objects pulled by rubber bands. The mass of object 2 is 36 kg. What are the masses of objects 1 and 3?

- A) 14 kg and 90 kg
- B) 72 kg and 18 kg
- C) 90 kg and 18 kg
- D) 14 kg and 72 kg

Answer: A

Var: 50+

16) An object accelerates at 4.1 m/s2 under the action of two rubber bands. What will be the object’s acceleration if it is pulled by four rubber bands?

- A) 8.2 m/s2
- B) 16 m/s2
- C) 4.1 m/s2
- D) 2.1 m/s2

Answer: A

Var: 50+

17) An object accelerates at 7.0 m/s2 under the action of two rubber bands. What will be the acceleration of two of these objects glued together if they are pulled by four rubber bands?

- A) 7.0 m/s2
- B) 14 m/s2
- C) 28 m/s2
- D) 3.5 m/s2

Answer: A

Var: 50+

18) Joe and Bill are playing tug-of-war. Joe is pulling with a force of 200 N. Bill is simply hanging on to the rope. Neither person is moving. What is the tension of the rope?

- A) 200 N
- B) 400 N
- C) 0 N
- D) 300 N

Answer: A

Var: 1

19) The figure shows two forces of equal magnitude acting on an object. If the common magnitude of the forces is 4.6 N and the angle between them is 40°, what third force will cause the object to be in equilibrium?

- A) 8.6 N pointing to the right
- B) 7.0 N pointing to the right
- C) 4.3 N pointing to the right
- D) 3.5 N pointing to the right

Answer: A

Var: 50+

20) Under the action of a constant force an object accelerates at 7.8 m/s2. What will the acceleration be if (a) The force is halved? (b) The object’s mass is halved? (c) The force and the object’s mass are both halved? (d) The force is halved and the object’s mass is doubled?

- A) (a) 3.9 m/s2, (b) 16 m/s2, (c) 7.8 m/s2, (d) 2.0 m/s2
- B) (a) 16 m/s2, (b) 3.9 m/s2, (c) 2.0 m/s2, (d) 7.8 m/s2
- C) (a) 3.9 m/s2, (b) 16 m/s2, (c) 2.0 m/s2, (d) 7.8 m/s2
- D) (a) 3.9 m/s2, (b) 16 m/s2, (c) 7.8 m/s2, (d) 7.8 m/s2

Answer: A

Var: 50+

**4.2 True/False**

** **

1) You throw a stone vertically upward, and it feels no air resistance. Once it is free of your hand but moving upward, the two forces acting on it are the downward pull of gravity and the upward force due to its motion.

Answer: FALSE

Var: 1

2) If a 5.0 kg box is pulled simultaneously by a 10.0 N force and a 5.0 N force, then its acceleration must be 3.0 m/s2.

Answer: FALSE

Var: 1

3) In a collision between a huge SUV and a small compact car, the SUV exerts a larger force on the compact than the compact exerts on the SUV.

Answer: FALSE

Var: 1

4) A box is placed on a table which rests on the floor. The box pushes on the table; the reaction force to the box’s push on the table is the table’s push on the floor.

Answer: FALSE

Var: 1

5) In order to get an object moving, you must push harder on it than it pushes back on you.

Answer: FALSE

Var: 1

6) If you pound a feather with a hammer, the feather always pushes on the hammer just as hard as the hammer pushes on the feather.

Answer: TRUE

Var: 1

7) A satellite is in orbit around the earth. The satellite pulls just as hard on the earth as the earth pulls on the satellite.

Answer: TRUE

Var: 1

8) When a small car is towing a large car by a very light (massless) horizontal rope, the rope exerts equal size forces on both cars.

Answer: TRUE

Var: 1

9) You pull on a crate with a rope. If the crate moves, the rope’s pull on the crate must have been larger than the crate’s pull on the rope, but if the crate does not move, both of these pulls must have been equal.

Answer: FALSE

Var: 1

10) In order to lift a bucket of concrete, you must pull up harder on the bucket than it pulls down on you.

Answer: FALSE

Var: 1

11) If the rockets of a spaceship in outer space (far from all gravity) suddenly lose power and go off, the spaceship will gradually slow to a stop.

Answer: FALSE

Var: 1

12) You are in a train traveling on a horizontal track and notice that a piece of luggage starts to slide toward the front of the train. From this observation, you can conclude that this train is not an inertial reference frame because it is slowing down.

Answer: TRUE

Var: 1

13) While flying horizontally in an airplane, you notice that a string dangling from the luggage compartment hangs at rest at 15 degrees away from the vertical. Using this observation, you can conclude that the airplane is an inertial reference frame because the string is not moving.

Answer: FALSE

Var: 1

14) An elevator suspended by a vertical cable is moving downward but slowing down. The tension in the cable must be greater than the weight of the elevator.

Answer: TRUE

Var: 1

15) A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all the forces acting on this crate must point down the ramp.

Answer: FALSE

Var: 1

16) A bucket is being lowered by a rope with a constant downward acceleration. The tension in the rope must be equal to the weight of the bucket.

Answer: FALSE

Var: 1

**4.3 Conceptual**

** **

1) Three children pull on a toy in three different directions, yet the toy does not move. Explain how this could be possible.

Answer: As long as the vector sum of all of the individual forces is equal to zero, there is no net force on the toy, so it does not move.

Var: 1

2) Consider what happens when you jump up in the air. Which of the following is the most accurate statement?

- A) It is the upward force exerted by the ground that pushes you up, but this force can never exceed your weight.
- B) You are able to spring up because the earth exerts a force upward on you which is stronger than the downward force you exert on the earth.
- C) Since the ground is stationary, it cannot exert the upward force necessary to propel you into the air. Instead, it is the internal forces of your muscles acting on your body itself which propels the body into the air.
- D) When you push down on the earth with a force greater than your weight, the earth will push back with the same magnitude force and thus propel you into the air.

Answer: D

Var: 1

3) A small car and an SUV are at a stoplight. The car has a mass equal to half that of the SUV, and the SUV’s engine can produce a maximum force equal to twice that of the car. When the light turns green, both drivers floor it at the same time. Which vehicle pulls ahead of the other vehicle after a few seconds?

- A) the car
- B) the SUV
- C) It is a tie.

Answer: C

Var: 1

4) An object is moving to the right in a straight line. The net force acting on the object is also directed to the right, but the magnitude of the force is decreasing with time. The object will

- A) continue to move to the right, with its speed increasing with time.
- B) continue to move to the right, with its speed decreasing with time.
- C) continue to move to the right with a constant speed.
- D) stop and then begin moving to the left.

Answer: A

Var: 1

5) You are making a circular turn in your car when you hit a big patch of ice, causing the force of friction between the tires and the road to become zero. While the car is on the ice, it

- A) moves along a straight-line path.
- B) continues to follow a circular path, but with a radius larger than the original radius.
- C) moves along a path that is neither straight nor circular.
- D) continues to follow the same circular path as initially.

Answer: A

Var: 1

6) A stalled car is being pushed up a hill by three people, and it is moving at a constant speed. The net force on the car is

- A) zero.
- B) in the same direction of the car’s motion.
- C) in the opposite direction of the car’s motion.
- D) None of the above

Answer: A

Var: 1

7) Suppose you are playing hockey on a new-age ice surface in which there is no friction between the ice and the hockey puck. You wind up and hit the puck as hard as you can. Just after the puck loses contact with your stick, the puck

- A) will not slow down or speed up.
- B) will start to slow down.
- C) will speed up a little, and then slow down.
- D) will speed up a little, and then move at a constant speed.

Answer: A

Var: 1

8) A ball is tossed vertically upward. When it reaches its highest point (before falling back downward),

- A) the velocity is zero, the acceleration is directed downward, and the force of gravity acting on the ball is directed downward.
- B) the velocity is zero, the acceleration is zero, and the force of gravity acting on the ball is zero.
- C) the velocity is zero, the acceleration is zero, and the force of gravity acting on the ball is directed downward.
- D) None of the above

Answer: A

Var: 1

9) A person gives a shopping cart an initial push along a horizontal floor to get it moving, and then lets go. The cart travels forward along the floor, gradually slowing as it moves. Consider the *horizontal force(s)* on the cart while it is moving forward and slowing. Which of the following statements is correct?

- A) Both a forward and a backward force are acting on the cart, but the forward force is larger.
- B) Both a forward and a backward force are acting on the cart, but the backward force is larger.
- C) Only a forward force is acting, which diminishes with time.
- D) Only a backward force is acting, no forward force.

Answer: D

Var: 1

10) Two bodies P and Q on a perfectly smooth horizontal surface are connected by a light cord. The mass of P is greater than that of Q. A horizontal force is applied to Q as shown in the figure, accelerating the bodies to the right.

The magnitude of the force exerted by the connecting cord **on body P** will be

- A) zero.
- B) less than F but not zero.
- C) equal to F.
- D) greater than F.

Answer: B

Var: 1

11) Explain, in terms of Newton’s Laws, why a quick jerk on a string may cause it to break, while the same change in momentum performed over a longer time will not.

Answer: Since F = , for a given momentum change ΔP the force F will decrease as the time ΔT increases. Thus, the stronger force experienced with a quick jerk may be enough to break the string.

Var: 1

12) In outer space, an astronaut is working with two pieces of equipment that are outwardly identical. However, one of the objects has a slightly larger mass than the other. Since objects are weightless in space, how can the astronaut distinguish between the two objects?

Answer: The objects are weightless in space, but they still have different, non-zero masses. The more massive object will require more effort to accelerate (since F = ma).

Var: 1

13) An object is moving to the right, and experiencing a net force that is directed to the right. The magnitude of the force is decreasing with time. The speed of the object is

- A) increasing.
- B) decreasing.
- C) constant in time.

Answer: A

Var: 1

14) If you jumped out of a plane, you would begin speeding up as you fall downward. Eventually, due to wind resistance, your velocity would become constant with time. After this occurs, the magnitude of the force of wind resistance is

- A) equal to the force of gravity acting on you.
- B) is much smaller than the force of gravity acting on you.
- C) is slightly smaller than the force of gravity acting on you.
- D) is greater than the force of gravity acting on you.

Answer: A

Var: 1

15) An object is moving with a constant velocity. Which statement(s) MUST be true?

- A) The net force on the object is zero.
- B) A small net force is acting on the object, in the direction of motion.
- C) No forces are acting on the object.
- D) Two of the above statements are true.

Answer: A

Var: 1

16) A woman is straining to lift a large crate, without success. It is too heavy. We denote the forces on the crate as follows: P is the upward force being exerted on the crate by the person, C is the contact force on the crate by the floor, and W is the weight of the crate.

How are the magnitudes of these forces related, while the person is trying unsuccessfully to lift the crate?

- A) P + C = W
- B) P + C < W
- C) P + C > W
- D) P = C

Answer: A

Var: 1

17) Suppose the force of wind resistance is proportional to the speed of the object and in the direction opposite the object’s velocity. If you throw an object upward, when is the magnitude of the acceleration the highest?

- A) It is highest right after the object is released.
- B) It is highest at the top of its trajectory.
- C) The acceleration of the object is the same throughout the entire trajectory.

Answer: A

Var: 1

18) A dog is standing in the tail bed of a pickup truck. The tail bed is coated with ice, causing the force of friction between the dog and the truck to be zero. The truck is initially at rest, and then accelerates to the right, moving along a flat road. As seen from a stationary observer (watching the truck move to the right), the dog

- A) does not move left or right, but simply slides toward the back of the truck.
- B) moves to the right, but not as quickly as the truck is moving to the right, causing it to slide toward the back of the truck.
- C) moves to the right at the same rate as the truck, so it doesn’t slide.
- D) moves to the left, as the truck moves to the right, causing the dog to slide toward the back of the truck.

Answer: A

Var: 1

19) A ball is thrown vertically upward, reaches a highest point, and comes back down. At the **top** of its path, what forces, if any, act on the ball? Explain your answer.

- A) no forces
- B) only a downward force
- C) only an upward force
- D) an upward and a downward force, opposing and equal

Answer: B

Var: 1

20) Your younger brother is supposed to mow the lawn using a push mower. He reasons from Newton’s Third Law that the mower will push back with the same force he exerts on the mower; therefore nothing will move and attempting to mow the lawn is pointless. What is wrong with his reasoning?

Answer: The boy exerts a force on the mower, but the “reaction force” is exerted by the mower __on the boy__. That is, the two forces are acting on different objects, and thus cannot cancel.

Var: 1

21) When decelerating quickly in a car, you feel as if you are being thrown forward in your seat. Which one of Newton’s Laws most directly explains this effect? Explain your reasoning.

Answer: Newton’s First Law is the best choice. Your body will remain in motion at the same velocity until an outside force (in this case provided by friction between your body and the seat) causes that velocity to change. Remember that you are not a part of the car – it will slow down before you do.

Var: 1

22) Newton’s Third Law suggests that a book sitting on a flat table experiences an upward force due to the table. If this is true, why doesn’t the book start moving upward?

Answer: The force exerted on the book by the table is a reaction force resulting from the weight of the book acting on the table. The net force acting on the book is zero, so the book does not move.

Var: 1

23) A large truck collides head-on with a cyclist. During the collision

- A) the truck exerts the same amount of force on the cyclist as the cyclist exerts on the truck.
- B) the truck exerts a greater amount of force on the cyclist than the cyclist exerts on the truck.
- C) the truck exerts a smaller amount of force on the cyclist than the cyclist exerts on the truck.
- D) the truck exerts a force on the cyclist, but the cyclist exerts no force on the truck.

Answer: A

Var: 1

24) Bill and Susan are both standing on identical skateboards (with really good ball bearings), initially at rest. Bill weighs three times as much as Susan. Bill pushes horizontally on Susan’s back, causing Susan to start moving away from Bill. Immediately after Bill stops pushing,

- A) Susan and Bill are moving away from each other, and Susan’s speed is three times that of Bill.
- B) Susan is moving away from Bill, and Bill is stationary.
- C) Susan and Bill are moving away from each other, with equal speeds.
- D) Susan and Bill are moving away from each other, and Susan’s speed is three times less than that of Bill.

Answer: A

Var: 1

*College Physics, 2e*** (Knight)**

**Chapter 11 Using Energy**

** **

**11.1 Quantitative**

** **

1) You have a flask of liquid nitrogen at a temperature of -243°C. You then heat the nitrogen until its temperature is doubled. What is the new temperature?

- A) 486°C
- B) -213°C
- C) -486°C
- D) None of the above

Answer: B

Var: 1

2) A person reading a European newspaper finds that the low temperature the night before in Stockholm was -16°C. What is the equivalent temperature in degrees Fahrenheit?

- A) 3.20000076°F
- B) -28.799999°F
- C) 23.1°F
- D) 8.9°F

Answer: A

Var: 40

3) A thermometer flashes the temperature in Celsius and Fahrenheit along with the time. If it flashes 25°F, what will the thermometer flash in Celsius?

- A) -3.9°C
- B) -18.1°C
- C) 77°C
- D) 13.9°C

Answer: A

Var: 50+

4) A laboratory experiment is to be run at 42.0 K. Express this temperature in Celsius to the nearest degree.

- A) -231°C
- B) 315°C
- C) 74°C
- D) 415°C

Answer: A

Var: 50+

5) A Carnot-efficiency engine operating between a reservoir of liquid mercury at its melting point and a colder reservoir extracts 15.0 J of heat from the mercury and does 4.0 J of work during each cycle. What is the temperature of the colder reservoir? Mercury melts at 233 K.

- A) 171 K
- B) 62 K
- C) 47 K
- D) 67 K

Answer: A

Var: 50+

6) What is the maximum efficiency of an engine operating between a reservoir in which ice and water coexist, and a reservoir in which water and steam coexist? The pressure is constant at 1.0 atmosphere for both.

- A) 27%
- B) 0.27%
- C) 100%
- D) 1.0%

Answer: A

Var: 1

7) A system has a heat source supplying heat at a rate of 187 W and is doing work at a rate of 130.899998 W. At what rate is the internal energy of the system changing?

- A) 56.1000022 W
- B) 317.900009 W
- C) -56.100002 W
- D) 187 W

Answer: A

Var: 50+

8) A perfectly insulated system has work done by it at a rate of 13 W. At what rate is the internal energy of the system changing?

- A) – 13 W
- B) 13 W
- C) 0 W
- D) 6.5 W

Answer: A

Var: 50+

9) A fluid in an insulated, flexible bottle is heated by a high resistance wire and expands. If 9 kJ of heat is applied to the system and it does 5 kJ of work, how much does the internal energy change?

- A) 4 kJ
- B) 14 kJ
- C) -4 kJ
- D) 45 kJ

Answer: A

Var: 50+

10) What is the average kinetic energy of an ideal gas at 842 K? (The value of Boltzmann’s constant is 1.38 × 10-23 J/K.)

- A) 1.74 × 10-20J
- B) 5.81 × 10-21J
- C) 1.18 × 10-17J
- D) 3.93 × 10-19J

Answer: A

Var: 50+

11) A heat engine operates between Tc = 294 K and Th = 450 K. What is the maximum possible efficiency?

- A) 0.35
- B) 0.65
- C) 0.53
- D) 1.53

Answer: A

Var: 50+

12) A heat engine has a maximum possible efficiency of 0.800. If it operates between a deep lake with a constant temperature of 287.0 K and a hot reservoir, what is the temperature of the hot reservoir?

- A) 1440 K
- B) 359 K
- C) 517 K
- D) 646 K

Answer: A

Var: 50+

13) A Carnot engine extracts 508 J of heat from a high-temperature reservoir during each cycle, and rejects 303 J of heat to a low-temperature reservoir during the same cycle. What is the efficiency of the engine?

- A) 0.4
- B) 0.68
- C) 1.68
- D) 0.63

Answer: A

Var: 50+

14) A nuclear power plant has an actual efficiency of 39%. If 0.24999999 MW of energy are released from fission, how much electric power does the power plant produce?

- A) 0.097 MW
- B) 9.7 MW
- C) 35 MW
- D) 0.35 MW

Answer: A

Var: 50+

15) A Carnot engine operates between a high temperature reservoir at 435 K and a river with water at 280 K. If it absorbs 3700 J of heat each cycle, how much work per cycle does it perform?

- A) 1318 J
- B) 2382 J
- C) 1449 J
- D) 2251 J

Answer: A

Var: 50+

16) A refrigerator with a COP of 3.7 cools to 9.0°C. What is the high temperature, Th, needed to operate the refrigerator at 9.0°C?

- A) 85°C
- B) 1052°C
- C) 11°C
- D) 42°C

Answer: A

Var: 50+

17) A heat pump with a COP of 4.90000007 absorbs heat from the atmosphere at a rate of

30 kW. At what rate is it doing work?

- A) 6 kW
- B) 147 kW
- C) 117 kW
- D) 36 kW

Answer: A

Var: 50+

18) A Carnot engine operating between a warmer unknown temperature and a reservoir of boiling helium at 1.76 K has an efficiency of 11.0%. What is the warmer temperature?

- A) 1.98 K
- B) 0.180 K
- C) 157 K
- D) 0.160 K

Answer: A

Var: 16

19) A Carnot engine operates between two reservoirs with unknown temperatures. If the Carnot engine operates at 43% efficiency, what is the ratio of the kelvin temperatures of the reservoirs, Tc/Th?

- A) 0.57
- B) 0.0021
- C) 0.0016
- D) 0.42999999

Answer: A

Var: 42

**11.2 True/False**

** **

1) A heat engine that is 40% efficient and has a heat input of 200 J per cycle at the hot reservoir will waste 80 J of heat each cycle.

Answer: FALSE

Var: 1

2) A refrigerator increases the entropy of its hot reservoir at the same time as it decreases the entropy of its cold reservoir, but a heat engine does just the opposite.

Answer: TRUE

Var: 1

3) As you increase the *difference* between the temperatures of the hot and cold reservoirs, a Carnot engine converts a larger and larger percent of the heat put into it into work.

Answer: TRUE

Var: 1

4) Heat can be transformed into work with 100% efficiency, but work cannot be transformed into heat with 100% efficiency.

Answer: FALSE

Var: 1

5) A Carnot engine operating between heat reservoirs at 10°C and 40°C has an efficiency of 75%.

Answer: FALSE

Var: 1

6) If two different gases are at the same temperature, the average translational kinetic energy per molecule must be the same for both of them.

Answer: TRUE

Var: 1

7) All real heat engines are less efficient than the Carnot engine.

Answer: TRUE

Var: 1

8) A 20% efficient heat engine that must do 50 J of work each cycle requires a heat input of 250 J per cycle.

Answer: TRUE

Var: 1

9) Just as a heat engine is more and more effective as its efficiency approaches 1, a refrigerator is more and more effective as its coefficient of performance approaches 1.

Answer: FALSE

Var: 1

10) Water turns to ice when it is placed in a freezer. During this process, the entropy of this water has decreased.

Answer: TRUE

Var: 1

**11.3 Conceptual**

** **

1) Is temperature a macroscopic or a microscopic concept?

Answer: Macroscopic

Var: 1

2) Is liberating heat through combustion a reversible or an irreversible process?

Answer: Irreversible

Var: 1

3) Does an increase in entropy increase or decrease the ability of a system to do work?

Answer: Decrease

Var: 1

4) Which of the following is a TRUE statement?

- A) The second law of thermodynamics is a consequence of the first law of thermodynamics.
- B) It is possible for heat to flow spontaneously from a hot body to a cold one or from a cold one to a hot one, depending on whether or not the process is reversible or irreversible.
- C) It is not possible to convert work entirely into heat.
- D) It is impossible to transfer heat from a cooler to a hotter body.
- E) All of these statements are false.

Answer: E

Var: 1

5) An important feature of the Carnot cycle is that

- A) its efficiency can be 100%.
- B) its efficiency depends only on the absolute temperature of the hot reservoir used.
- C) its efficiency is determined by the temperatures of the hot and cold reservoirs between which it works and by the properties of the working substance used, and on nothing else.
- D) it is an example of an irreversible process that can be analyzed exactly without approximations.
- E) no engine can be more efficient than a Carnot engine operating between the same two temperatures.

Answer: E

Var: 1

6) Which of the following is a FALSE statement?

- A) Entropy is a quantitative measure of disorder.
- B) The total entropy change in one cycle of a Carnot engine is zero.
- C) The entropy of an isolated system is conserved, i.e., constant.
- D) Entropy can be measured in units of J/K.

Answer: C

Var: 1

7) Which of the following relationships are true for *all* types of heat engines? (There may be more than one correct choice.)

- A) e = 1 –
- B) e =
- C) e =
- D) =
- E) e = 1 –

Answer: B, C, E

Var: 1

*College Physics, 2e*** (Knight)**

**Chapter 21 Electric Potential**

** **

**21.1 Quantitative**

** **

1) A 6.0 μC negative charge is attracted to a large, well-anchored, positive charge. How much kinetic energy does the negatively charged object gain if the potential difference through which it moves is 3 mV?

- A) 18 nJ
- B) 0.50 kJ
- C) 0.50 J
- D) 6.0 μJ

Answer: A

Var: 30

2) A sphere with radius 2.0 mm carries a 1.0 μC charge. What is the potential difference, VB – VA, between point B 4.0 m from the center of the sphere and point A 9.0 m from the center of the sphere? (The value of k is 9.0 ´ 109 N·m2/C2.)

- A) 1300 V
- B) -1300 V
- C) 140 V
- D) -0.45 V

Answer: A

Var: 50+

3) A 3.0 μC point charge and a 9.0 μC point charge are initially infinitely far apart. How much work does it take to bring the 3.0 μC point charge to x = 3.0 mm, y = 0.0 mm, and the 9.0 μC point charge to x = -3.0 mm, y = 0.0 mm? (The value of k is 9.0 ´ 109 N·m2/C2.)

- A) 41 J
- B) 81 J
- C) 27 J
- D) 6.8 J

Answer: A

Var: 12

4) A dipole with ±6.0 μC charges is positioned so that the positive charge is 1.0 mm to the right of the origin and the negative charge is at the origin. How much work does it take to bring a

10.0 μC charge from infinity to a position x = 3.0 mm, y = 0.0 mm? (The value of k is 9.0 ´ 109 N·m2/C2.)

- A) 90 J
- B) 450 J
- C) 75 J
- D) 200 J

Answer: A

Var: 50+

5)

Point charges, Q1 = +46 nC and Q2 = -75 nC, are placed as shown. In the figure, an external force transports an electron from point A to point B. The work done by the external force is closest to:

- A) + 730 eV
- B) + 610 eV
- C) + 480 eV
- D) – 730 eV
- E) – 480 eV

Answer: A

Var: 50+

6) A proton with a speed of 2.0 x 105 m/s falls through a potential difference V and thereby increases its speed to 4.0 × 105 m/s. Through what potential difference did the proton fall?

- A) 630 V
- B) 210 V
- C) 840 V
- D) 1000 V
- E) 100 V

Answer: A

Var: 24

7) A proton with speed 1.5 × 105 m/s falls through a potential difference of 100 volts, gaining speed. What is the speed reached?

- A) 4.56 × 105m/s
- B) 2.04 × 105m/s
- C) 3.55 × 105m/s
- D) 8.80 × 105m/s
- E) 1.55 × 106m/s

Answer: B

Var: 1

8) A charge of 3.0 μC and a second charge are initially far apart. If it takes 29 J of work to bring them to a final configuration in which the 3.0 μC is at x = 1.0 mm, y – 1.0 mm, and the other charge is at x = 1.0 mm, y = 3.0 mm, find the magnitude of the unknown charge. (The value of k is 9.0 ´ 109 N·m2/C2.)

- A) 2.15 μC
- B) 4.30 μC
- C) 10.74 μC
- D) 4.30 nC

Answer: A

Var: 50+

9) Consider the group of charges in this figure. All three charges have Q = 2.4 nC. What is their electric potential energy?

- A) 4.1 × 10-6 J
- B) 4.6 × 10-6 J
- C) 4.2 × 10-6 J
- D) 4.4 × 10-6 J

Answer: A

Var: 50+

10) An electron was accelerated from rest through a potential difference of 9900 V. What is its speed?

- A) 5.9 × 107 m/s
- B) 4.9 × 107 m/s
- C) 3.9 × 107 m/s
- D) 2.9 × 107m/s

Answer: A

Var: 50+

11) Three charges form an equilateral triangle with 1.6 cm long sides. What is the electric potential at the point indicated with the dot?

- A) zero
- B) 3900 V
- C) 1900 V
- D) 5800 V

Answer: A

Var: 50+

12) Two parallel circular plates with radius 7.0 mm carrying equal-magnitude surface charge densities of ±3.0 μC/m2 are separated by a distance of 1.0 mm. How much stored energy do the plates have?

- A) 78 nJ
- B) 25 nJ
- C) 7.9 nJ
- D) 250 nJ

Answer: A

Var: 36

13) Two parallel plates are separated by 1.0 mm. If the potential difference between them is

3.0 V, what is the magnitude of their surface charge densities?

- A) 27 nC/m2
- B) 0.16 mC/m2
- C) 53 nC/m2
- D) 0.33 mC/m2

Answer: A

Var: 5

14) A 3.0 pF capacitor consists of two parallel plates that have surface charge densities of

±1.0 nC/mm2. If the potential between the plates is 23.0 kV, find the surface area of one of the plates.

- A) 69 mm2
- B) 0.014 mm2
- C) 35 mm2
- D) 0.0072 mm2

Answer: A

Var: 50+

15) Two parallel plates that are initially uncharged are separated by 1.2 mm. What charge must be transferred from one plate to the other if 11.0 kJ of energy are to be stored in the plates? The area of each plate is 19.0 mm2.

- A) 56 μC
- B) 39 μC
- C) 78 μC
- D) 3.5 mC

Answer: A

Var: 50+

16) A 100.0 pF capacitor consists of two circular plates of radius 0.40 mm. How far apart are the plates? (The value of εo is 8.85 ´ 10-12 C2/N·m2.)

- A) 0.044 μm
- B) 0.022 μm
- C) 0.0050 μm
- D) 0.0025 μm

Answer: A

Var: 28

17) A 1.0 μF capacitor has a potential difference of 6.0 V applied across its plates. If the potential difference across its plates is increased to 8.0 V, how much additional energy does the capacitor store?

- A) 14 μJ
- B) 28 μJ
- C) 2.0 μJ
- D) 4.0 μJ

Answer: A

Var: 28

18) A parallel-plate capacitor consists of two parallel, square plates that have dimensions 1.0 cm by 1.0 cm. If the plates are separated by 1.0 mm, and the space between them is filled with teflon, what is the capacitance? (The dielectric constant for teflon is 2.1.)

- A) 1.9 pF
- B) 0.44 pF
- C) 2.1 pF
- D) 0.88 pF

Answer: A

Var: 5

19) A parallel-plate capacitor has a potential energy due to its charge of 6.00 mJ. It is accidentally filled with water in such a way as not to discharge its plates. How much energy does it continue to store after it is filled? (The dielectric constant for water is 78 and for air is 1.0006.)

- A) 0.077 mJ
- B) 468 mJ
- C) 0.04 mJ
- D) 6.00 mJ

Answer: A

Var: 18

20) A parallel-plate capacitor has a voltage of 391 V applied across its plates, then the voltage source is removed. What is the voltage across its plates if the space between them becomes filled with mica? (The dielectric constant for mica is 5.4 and for air is 1.0006.)

- A) 72 V
- B) 2110 V
- C) 641 V
- D) 18,675 V

Answer: A

Var: 50+

21) A uniform electric field has the strength of 5.0 N/C. What is the electric energy density of the field? (The value of εo is 8.85 ´ 10-12 C2/N·m2.)

- A) 1.1 × 10-10J/m3
- B) 2.2 × 10-11J/m3
- C) 1.4 × 1012J/m3
- D) 2.8 × 1012J/m3

Answer: A

Var: 5

22) A small object carries a charge of 10.0 μC. If the object is so small that it can be regarded as a point charge, what is the energy density at a distance of 2.0 m from the charge? (The value of k is 9.0 ´ 109 N·m2/C2.)

- A) 2.2 mJ/m3
- B) 4.5 mJ/m3
- C) 9.0 mJ/m3
- D) 18 mJ/m3

Answer: A

Var: 40

**21.2 True/False**

** **

1) Suppose you have two positive point charges and want to move them closer together. To do the least amount of work, you should move them directly toward each other; any other path will require more work because the charges must move through a greater distance.

Answer: FALSE

Var: 1

2) Two equal positive charges are separated by a fixed distance. If you put a third positive charge midway between these two charges, its electrical potential energy (relative to infinity) is zero because the electrical forces due to the two fixed charges just balance each other.

Answer: FALSE

Var: 1

3) You want to put an electron somewhere between the plates of a parallel plate capacitor so that it will have the maximum electrical potential energy relative to one of the plates. The best place to put it is at the inner surface of the negative plate.

Answer: TRUE

Var: 1

4) Suppose you have two point charges, +Q and -q. As you pull them farther and farther apart, you increase the potential energy of this system relative to infinity.

Answer: TRUE

Var: 1

5) If the electric field is zero everywhere inside a region of space, the potential must also be zero in that region.

Answer: FALSE

Var: 1

6) If the electrical potential in a region is constant, the electric field must be zero everywhere in that region.

Answer: TRUE

Var: 1

7) The potential is zero on the surface of a conductor in electrostatic equilibrium.

Answer: FALSE

Var: 1

8) When the electric field is zero at a point, the potential must also be zero there.

Answer: FALSE

Var: 1

9) If the potential is constant on a surface, then any electric field present can only be perpendicular to that surface.

Answer: TRUE

Var: 1

10) If an object is at zero potential, it must be uncharged.

Answer: FALSE

Var: 1

11) Two equal but opposite point charges are held a distance D apart, and a third point charge Q is placed midway between them. When Q is released it will remain at rest because its potential energy is zero at the midpoint.

Answer: FALSE

Var: 1

12) Four identical positive point charges lie at the corners of a square. The electrical potential at the center of this square is zero because the electric fields all cancel at that point.

Answer: FALSE

Var: 1

**21.3 Conceptual**

** **

1) Four charged particles (two having a charge +Q and two having a charge -Q) are distributed on the xy-plane, as shown below. Each charge is equidistant from the origin. The voltage is zero at infinity. The voltage at location P, which is on the z axis, is

- A) zero.
- B) positive.
- C) negative.
- D) impossible to determine based on the information given.

Answer: A

Var: 1

2) Four charged particles (two having a charge +Q and two having a charge -Q) are distributed on the xy-plane, as shown below. Each charge is equidistant from the origin. The voltage is zero at infinity. The amount of work required to move a positively charged particle from point P to point O (which is on the *z*-axis, below the origin) is

- A) zero.
- B) positive.
- C) negative.
- D) dependent on the path in which the charged is moved.

Answer: A

Var: 1

3) As an electron moves from a high potential to a low potential, its electrical potential energy

- A) increases.
- B) decreases.
- C) remains constant.

Answer: A

Var: 1

4) A parallel plate capacitor contains a positively charged plate on the left, and a negatively charged plate on the right. An electron in between the plates is moving to the right. Which statement is true?

- A) The potential energy of the electron is increasing and it is moving to a region having a lower potential.
- B) The potential energy of the electron is increasing and it is moving to a region having a higher potential.
- C) The potential energy of the electron is decreasing and it is moving to a region having a lower potential.
- D) The potential energy of the electron is decreasing and it is moving to a region having a higher potential.

Answer: A

Var: 1

5) The capacitance of a capacitor depends on

- A) the charge on it.
- B) the potential difference across it.
- C) the energy stored in it.
- D) More than one of these
- E) None of these

Answer: E

Var: 1

6) Suppose a region of space has a uniform electric field, directed toward the right, as shown in the figure. Which statement is true?

- A) The voltage at all three locations is the same.
- B) The voltage at points A and B are equal, and the voltage at point C is higher than the voltage at point A.
- C) The voltage at points A and B are equal, and the voltage at point C is lower than the voltage at point A.
- D) The voltage at point A is the highest, the voltage at point B is the second highest, and the voltage at point C is the lowest.
- E) None of the above

Answer: C

Var: 1

7) If the voltage at a point in space is zero, then the electric field must be

- A) negative.
- B) zero.
- C) uniform.
- D) positive.
- E) Impossible to determine based on the information given.

Answer: E

Var: 1

8) A parallel-plate capacitor having circular plates of diameter D and a distance d apart stores energy U when it is connected across a fixed potential difference. If you want to triple the amount of energy stored in this capacitor by changing only the size of its plates, the diameter should be changed to:

- A) 9D
- B) 3D
- C) D
- D)
- E)

Answer: C

Var: 1

9) A hydrogen atom consists of a proton and an electron. If the orbital radius of the electron increases, the potential energy of the electron

- A) increases.
- B) decreases.
- C) remains the same.
- D) depends on the zero point of the potential.

Answer: A

Var: 1

10) A proton is accelerated from rest through a potential difference Vo and gains a speed vo. If it were accelerated instead through a potential difference of 2Vo, it would gain a speed:

- A) 8 vo
- B) 4 vo
- C) 2 vo
- D) vo

Answer: D

Var: 1

11) A proton is projected toward a fixed nucleus of charge +Ze with velocity vo. Initially the two particles are very far apart. When the proton is a distance R from the nucleus its velocity has decreased to 1/2 vo. How far from the nucleus will the proton be when its velocity has dropped to 1/4 vo?

- A) 1/16 R
- B) 1/4 R
- C) 1/2 R
- D) 4/5 R
- E) None of these

Answer: D

Var: 1

12) Two conductors are joined by a long copper wire. Thus

- A) each conductor carries the same free charge.
- B) each conductor must be at the same potential.
- C) the electric field at the surface of each conductor is the same.
- D) no free charge can be present on either conductor.
- E) the potential on the wire is the average of the potential of each conductor.

Answer: B

Var: 1

## Reviews

There are no reviews yet.