Download Work, Energy, and Power Practice key

WORK, POWER & ENERGY REVIEW
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WORK& POWER
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1. If the sign of work is negative,
a. the force is in the same direction as the displacement.
b. the force is perpendicular to the displacement.
c. the component of the force that does work is in the direction opposite the displacement.
d. the component of the force that does work is perpendicular to the displacement.
2. A painter lifts a bucket of paint, carries it 5 m horizontally, then sets it back down. Which of the
following is true?
a. The force of gravity does negative work when the worker lifts the bucket.
b. The painter does positive work on the bucket when carrying it horizontally at constant speed.
c. The painter does positive work on the bucket when setting it down.
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d. No net work is done on the bucket.
3. A parachutistfalls at a constant speed for 200 m. Which of the following is true?
a. The force of gravity is the only force dOing work on the parachutist.
b. Air resistance is the only force doing work on the parachutiSt.
c. No forces are doing work on the parachutist.
d. No net work is done on the parachutist.
4. Which of the following is not a valid equation for power?
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5. If a machine increases the distance over which work is done,
a. the force required to do the work is less.
b. the force required to do the work is greater.
c. the force required to do the work is the same.
d. the amount of work done is increased.
6. If a machine decreases the distance over which work is done,
a. the work the machine does is less.
b. the work the machine does is greater.
c. the work the machine does is the same.
7.
A construction worker lifts a heavy cinder block 1 m off the ground, holds it in place for 3 s, then sets it
back down in the same place. Describe the forces doing work on the block and the net work on the block
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How much work is done if you raise a 5.0 kg mass 1.5 m above the ground?
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Two students are moving 80 N cartons of books from the floor onto a platform. One student
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How much power is developed by an electric motor that moves a 500 N load a distance of 20 m
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A child pulls a wagon 3.0 m using a force of 55 N at an angle 35° above horizontal. The force of
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A parachutist falls for 20 m. The parachutist weighs 800 N and feels a frictional force of 200 N.
What is the net work done on the skydiver during her fall?
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15. How does the kinetic energy of an object change if the object's speed doubles?
a. The kinetic energy decreases to half its original value.
b. The kinetic energy doubles.
c. The kinetic energy increases by a factor of 4.
d. The kinetic energy does not change.
~ 16. The work-kinetic energy theorem states that
a. the net work done on an object equals the kinetic energy of the object.
b. the net work done on an object equals the change in the kinetic energy of the object.
c. the change in the net work done on an object equals the kinetic energy of the object.
d. the change in the net work done on an object equals the change in the kinetic energy of the
object.
~ 17. Friction does -400 J of net work on a moving car. How does this affect the kinetic energy of the car?
a. The kinetic energy increases by 400 J.
b. The kinetic energy decreases by 400 J.
c. The kinetic energy decreases by 160 kJ.
d. The kinetic energy does not change.
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18. How does the elastic potential energy in a mass-spring system change if the displacement of the mass
is doubled?
a. The elastic potential energy decreases to half its original value.
b. The elastic potential energy doubles.
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c. The elastic potential energy increases
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d. The elastic potential energy does not change.
19. Mechanical energy is not conserved when
a. gravitational potential energy is converted to kinetic energy.
b. kinetic energy is converted to gravitational potential energy.
c. kinetic energy is converted to elastic potential energy.
d. friction is not negligible.
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20.
Which has the greater gravitational potential energy a 550 g
shelf or a 350 g flower pot sitting on a 1.8 m high shelf?
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A child having a mass of 35.0 kg is on a sled having a mass of 5.r!kg. If the child and
traveling together have a kinetic energy of 260 J, how fast are they moving?
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A 30.0 kg box initially sliding at 5.00 mls on a rough surface is brought to rest by 20.0 N
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23.
A 1.0 X 10' kg sports car is initially traveling at 15
m/s. The driver then applied the brakes for
several seconds so that -25,000 J of net work is done on the car. Calculate the initial kinetic energy of the
car. Then, use the work kinetic energy theorem to find the final speed of the car.
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A 0.250 kg block on a vertical spring with a spring constant of 5000 N/m is pushed
downward, compressing the spring 0.100 m. What is the EPE stored in the spring?
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25.
A tennis ball is thrown up into the air starting from a height of 1.5 m. The ball reaches a peak height, then
falls down to the ground. Assuming air resistance is negligible, describe the energy transfers that take
place during the flight of the ball and what work was done to transfer the energy. Is mechanical energy
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conserved in this situation? Why or why not?
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A ball is thrown upward. Describe changes in its mechanical energy, kinet1'cenergy, and
gravitational potential energy between the time the ball is released and the time it reaches its
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The largest apple ever grown had a mass of 1.47 kg. Suppose you hold such an apple in your
hand. You accidentally drop the apple, then manage to catch it just before it hits the ground. If
the speed of the apple at that moment is 5.42 mis, what is the kinetic energy of the apple?
From what height did you drop it?
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A pole vaulter clears a bar that is 6.00 m above the ground. With what velocity does the vaulteb
strike the mat in the landing area? (Disregard air resistance)
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