Multiple Choice
Identify the choice that best completes the statement or answers the question.
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1.
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A boy exerts an average force of 65 N when he lifts a box 1.2 meters. How much work does he do?
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a.
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0 J |
c.
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66 J |
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b.
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54 J |
d.
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78 J |
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2.
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How much power is required to do 180 J of work in 2.4 s?
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a.
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7.5 W |
c.
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178 W |
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b.
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75 W |
d.
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430 W |
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3.
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How much power is required to lift a 30.0 N chair 0.20 m in 2.0 s?
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a.
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1.0 W |
c.
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12 W |
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b.
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3.0 W |
d.
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15 W |
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4.
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What is the mechanical advantage of a single, fixed pulley?
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5.
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Calculate the gravitational potential energy relative to the ground when an 82 kg person climbs to the top of a 2.0 m stepladder.
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a.
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164 J |
c.
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402 J |
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b.
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3.3 ´ 102 J |
d.
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1.6 ´ 103 J |
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6.
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What is the kinetic energy of a 1.40 kg discus with a speed of 22.5 m/s?
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a.
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15.8 J |
c.
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354 J |
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b.
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31.5 J |
d.
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709 J |
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7.
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A dog running at a speed of 12 m/s has 1,080 J of kinetic energy. What is the mass of the dog?
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a.
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7.5 kg |
c.
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30 kg |
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b.
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15 kg |
d.
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45 kg |
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8.
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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 free-fall acceleration on the moon.
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a.
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0.15 m/s2 |
c.
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6.6 m/s2 |
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b.
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1.7 m/s2 |
d.
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9.8 m/s2 |
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9.
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_____ is the ratio of useful work output to work input.
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a.
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Potential energy |
c.
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Kinetic energy |
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b.
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Efficiency |
d.
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Power |
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10.
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How efficient is a machine that uses 130 J to lift a 50.0 N load 2.0 m?
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a.
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19% |
c.
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77% |
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b.
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52% |
d.
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87% |
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11.
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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?
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a.
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200 N |
c.
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zero |
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b.
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200 L |
d.
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None of the above |
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12.
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What are the units of work?
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a.
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J |
c.
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kg • m2/s2 |
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b.
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N • m |
d.
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All of the above |
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13.
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A weightlifter presses a 400 N weight 0.5 m over his head in 2 seconds. What is the power of the weightlifter?
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a.
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100 N |
c.
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400 watts |
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b.
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25 watts |
d.
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100 watts |
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14.
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What is the gravitational potential energy of a 54 kg box that is 8.0 m above the ground?
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a.
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5,500 J |
c.
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3,400 J |
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b.
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4,234 J |
d.
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550 J |
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15.
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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?
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a.
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zero |
c.
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2,100 J |
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b.
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75 J |
d.
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4,625 J |
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16.
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Which of the following processes requires the most work?
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a.
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A 10 kg weight rests on a table. |
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b.
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A person holds a 1 kg weight still with outstretched arms. |
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c.
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A person lifts a 1 kg weight 1 m off the floor. |
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17.
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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?
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a.
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165 N |
c.
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zero |
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b.
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220 J |
d.
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145 J |
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18.
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What are the units of power?
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a.
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watts |
c.
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joules per second |
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b.
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horsepower |
d.
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All of the above |
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19.
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Gravitational potential energy depends on
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a.
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the mass of the object. |
c.
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the acceleration due to gravity. |
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b.
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the height of the object. |
d.
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All of the above |
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20.
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A medicine ball has a mass of 5 kg and is thrown with a speed of 2 m/s. What is its kinetic energy?
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a.
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100 J |
c.
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2,000 J |
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b.
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10 J |
d.
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500 J |
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21.
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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?
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a.
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Both the kinetic and potential energy are decreasing. |
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b.
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The minimum kinetic energy is zero. |
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c.
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When the kinetic energy is zero, the potential energy will be 400 J greater. |
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d.
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The potential energy increases when the kinetic energy decreases. |
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22.
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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?
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a.
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6 m |
c.
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12 m |
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b.
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20 m |
d.
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40 m |
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