# Work Power Machines Test Review - TeacherWeb by xiuliliaofz

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Work, Power, and Simple Machines Test Review

Review: Momentum

1. Two astronauts, facing each other in outer space, push off each other. One astronaut has
a mass of 48 kg and the other astronaut has a mass of 40 kg. If the 40 kg astronaut heads
off with a velocity of 3.0 m/s to the right, what is the velocity of the 48 kg astronaut?

2. A) What is the change in momentum of the 40 kg astronaut?
B) What is the impulse on the 40 kg astronaut?
C) If the astronauts take 1.2 seconds to push off each other, what is the force that the 48
kg astronaut exerts on the 40 kg astronaut?

Work and Power

1. Russell drags his suitcase 15 meters at a constant speed with a horizontal force of 95.0 N.
How much work does Russell do to overcome the force of friction? If the floor has just been
waxed, does he have to do more work or less work to move the suitcase?

2. Russell then lifts the 15-kg suitcase a distance of 2 meters and carries it for 10 meters. How
much work does he do?

3. A 50-kg student climbs a 5.0-m high staircase in 3.0 seconds. What is the power?

4. If the student in #3 climbs the same stair case in 10 seconds, does the power change? Does
the work change?

5. A 60 W light bulb uses 3000 J of energy. How much time was it left on for?

6. How much energy in Joules would a 60 W bulb use if left on for an hour?

Simple Machines

1. A mover pushes a box up an inclined plane into the back of a truck. The height of the
inclined plane is 2 meters and the length is 4 meters. What is the mechanical advantage
of the inclined plane?
2. A lever has a mechanical advantage of 3. How heavy an object can a girl move if she
exerts a force of 100 N on the lever?
3. Ancient Egyptians used an inclined plane to move a 5000 N block to the top of the
pyramid. If the inclined plane had a mechanical advantage of 5, how much force did the
workers have to use to move the block?
4. A wizard pulls 30 meters of rope to lift up his magic cauldron using a pulley. If the
pulley has a mechanical advantage of 4, what distance does the magic cauldron move up?
5. A lever is used to lift a heavy load. When a 50-N force pushes one end of the lever down
1.2 m, the load rises 0.2 m. Calculate the weight of the load. (Assume no friction).
6. In raising a 500-N piano with a pulley system, the workers note that for every 2 m of rope
pulled down, the piano rises 0.4 m. Ideally (no friction), how much force is required to
lift the piano?
7. A person uses 200 J of work to drag a box up an inclined plane, and the inclined plane
does 150 J of work. What is the efficiency of the inclined plane? Why is the work output
less than the work input? Where did the extra energy go?
8. A pulley system operates with 40% efficiency. If the work put in is 200 Joules, how
much work is produced by the pulley system?
9. A wedge has an efficiency of 85%. If the wedge does 300 J of work, how much work
was applied to the wedge?
10. Using a lever, a person applies 60 N of force and moves the lever 1 meter. This moves a
200 N rock at the other end by 0.2 meters. What is the efficiency of the machine?
11. True or false: Simple machines make work easier by doing more work than was put into
them.
12. What is the difference between theoretical and actual mechanical advantage?
13. If the theoretical mechanical advantage of an inclined plane is 5 and the actual
mechanical advantage is 4.2, what is the efficiency of the inclined plane?
14. What is the mechanical advantage of the block and tackle (pulley system) in the margin?
15. What the advantage of using a fixed pulley? What is the advantage of using a movable
pulley?

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