Multiple Choice Identify the choice that best completes the statement or answers the question.


1.

A boy exerts an average force of 65 N when he lifts a box 1.2 meters. How much work does he do?
a.

0 J 
c.

66 J 
b.

54 J 
d.

78 J 


2.

How much power is required to do 180 J of work in 2.4 s?
a.

7.5 W 
c.

178 W 
b.

75 W 
d.

430 W 


3.

How much power is required to lift a 30.0 N chair 0.20 m in 2.0 s?
a.

1.0 W 
c.

12 W 
b.

3.0 W 
d.

15 W 


4.

What is the mechanical advantage of a single, fixed pulley?


5.

Calculate the gravitational potential energy relative to the ground when an 82 kg person climbs to the top of a 2.0 m stepladder.
a.

164 J 
c.

402 J 
b.

3.3 ´ 10^{2} J 
d.

1.6 ´ 10^{3} J 


6.

What is the kinetic energy of a 1.40 kg discus with a speed of 22.5 m/s?
a.

15.8 J 
c.

354 J 
b.

31.5 J 
d.

709 J 


7.

A dog running at a speed of 12 m/s has 1,080 J of kinetic energy. What is the mass of the dog?
a.

7.5 kg 
c.

30 kg 
b.

15 kg 
d.

45 kg 


8.

An astronaut with a mass of 91 kg is 0.30 m above the moon’s surface. The astronaut’s potential energy is 46 J. Calculate the freefall acceleration on the moon.
a.

0.15 m/s^{2} 
c.

6.6 m/s^{2} 
b.

1.7 m/s^{2} 
d.

9.8 m/s^{2} 


9.

_____ is the ratio of useful work output to work input.
a.

Potential energy 
c.

Kinetic energy 
b.

Efficiency 
d.

Power 


10.

How efficient is a machine that uses 130 J to lift a 50.0 N load 2.0 m?
a.

19% 
c.

77% 
b.

52% 
d.

87% 


11.

A boy pushes on a parked car with a force of 200 N. The car does not move. How much work does the boy do on the car?
a.

200 N 
c.

zero 
b.

200 L 
d.

None of the above 


12.

What are the units of work?
a.

J 
c.

kg • m^{2}/s^{2} 
b.

N • m 
d.

All of the above 


13.

A weightlifter presses a 400 N weight 0.5 m over his head in 2 seconds. What is the power of the weightlifter?
a.

100 N 
c.

400 watts 
b.

25 watts 
d.

100 watts 


14.

What is the gravitational potential energy of a 54 kg box that is 8.0 m above the ground?
a.

5,500 J 
c.

3,400 J 
b.

4,234 J 
d.

550 J 


15.

An object weighing 75 N is dropped from the top of a building and falls a distance of 28 m to the ground. How much work does gravity do on the object from the time it is dropped to the time it hits the ground?
a.

zero 
c.

2,100 J 
b.

75 J 
d.

4,625 J 


16.

Which of the following processes requires the most work?
a.

A 10 kg weight rests on a table. 
b.

A person holds a 1 kg weight still with outstretched arms. 
c.

A person lifts a 1 kg weight 1 m off the floor. 


17.

A man pushes a crate along a factory floor by exerting a force of 55 N. If the crate moves a distance of 4.0 m, how much work does the man perform?
a.

165 N 
c.

zero 
b.

220 J 
d.

145 J 


18.

What are the units of power?
a.

watts 
c.

joules per second 
b.

horsepower 
d.

All of the above 


19.

Gravitational potential energy depends on
a.

the mass of the object. 
c.

the acceleration due to gravity. 
b.

the height of the object. 
d.

All of the above 


20.

A medicine ball has a mass of 5 kg and is thrown with a speed of 2 m/s. What is its kinetic energy?
a.

100 J 
c.

2,000 J 
b.

10 J 
d.

500 J 


21.

A pendulum swings back and forth and has a kinetic energy of 400 J at a particular point in its path. Which of the following statements is not true?
a.

Both the kinetic and potential energy are decreasing. 
b.

The minimum kinetic energy is zero. 
c.

When the kinetic energy is zero, the potential energy will be 400 J greater. 
d.

The potential energy increases when the kinetic energy decreases. 


22.

The brakes on a car exert a frictional force of 6,000 N in getting the car to stop. If the work done by the brakes is 120,000 J in coming to a stop, how many meters does the car travel after the driver applies the brakes?
a.

6 m 
c.

12 m 
b.

20 m 
d.

40 m 
