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## Friction

Instructions: Read each question carefully. Choose the answer that best fits the question. Short answer response questions must be responded to in complete sentences. If the question involves calculations, you must show all your math work.

1.
Friction causes kinetic energy to be converted into
1. potential energy.
2. thermal energy.
3. mechanical energy.
4. electrical energy.
2.
If you turn the water off on a water slide, causing your brother to come to a stop half-way down, what caused his motion to stop?
1. inertia
2. momentum
3. friction
4. heat
3.
Which of the following does not involve any friction?
1. A bicycle rolling down a hill
2. A baseball player sliding into 2nd base
3. A diver falling through the air to a pool
4. All of the above experience some friction.
4.
The coefficient of static friction, $mu$, predicts the                      force of static friction.
5.
Morgan has a job working in a mine. She walks up and begins pushing a large rock that is sitting still. After a lot of shoving, she makes it start sliding across the floor. She pushes it to the edge of a cliff where it falls through the air onto a rolling conveyor belt which carries it to a machine to be crushed.

At which point did the rock have the strongest friction?
1. when it was sitting still
2. when Morgan was pushing it
3. when it was falling through the air
4. when it was rolling on the conveyor belt
6.
These two factors determine the strength of the force of friction.
1. speed and light
2. how fast the objects are going and on what planet
3. how big the objects are and how hard you push them
4. how hard the surfaces push together and the types of surfaces involved
7.
Sports shoes tend to have rough bottoms. What is the best explanation for this?
1. To decrease friction so you move faster
2. To increase friction so you can change your motion more easily
3. To decrease your mass so you have more momentum
4. To reduce gravity and make you lighter
8.
Brant pushes a toy car with a force of 50 N. The force of friction as the car moves is 5 N. What is the net force on the car?
1. 55 N
2. 45 N
3. 50 N
4. 10 N
9.
Why is it more efficient to move a a box up a ramp on wheels than sliding it?
1. Because wheels reduce the pull of gravity.
2. Because rolling friction is weaker than sliding friction, so you lose less work.
3. Because wheels increase the normal force on a box.
4. None of the above
10.
The coefficient of rolling friction, $mu$, depends on the size of the                 .
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