PHYS 231 Quiz #3

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 Cheat Sheet:
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		p=mv

		If an equation you need is not listed here, ask.

Multiple choice: 1 pt. each

1. A car skids to a halt. The work done by friction is

A. 0 J

B. positive

* C. negative

D. equal to the work done by gravity

2. A weightlifter lifts a dumbell from the floor to a stationary position above his head. In doing so, he

* A. changes the potential energy of the dumbell.

B. changes the kinetic energy of the dumbell.

C. does no work on the dumbell.

D. does all of the above.

3. Motor A delivers a greater level of power than Motor B. In order to do the same amount of work,

* A. Motor A takes less time than Motor B.

B. Motor A takes more time than Motor B.

C. Motor A takes the same amount of time as Motor B.

D. we need more information.

4. A mass attached to a spring oscillates back and forth on a frictionless table. When the spring is at its equilibrium length,

A. the speed of the mass is zero.

* B. the acceleration of the mass is zero.

C. the spring potential energy is at a maximum.

D. the total energy is zero.

5. Which of the following is a requirement for conservation of mechanical energy of a system?

A. The system is isolated.

B. No energy is added to or taken from the system.

C. There is no internal friction in the system.

* D. all of the above.

6. A mass is released from a point on a track and slides down and around a loop-the-loop. Let the height of the point of release be h, the radius of the track be R, and let h=2R. What happens?

A. The mass makes it around the loop-the-loop without falling.

B. The mass makes it to the top of the loop-the-loop and then falls.

* C. The mass falls before getting to the top of the loop-the-loop.

D. The mass makes it past the top of the loop-the-loop and then falls.

7. A bead slides on a wire. If it is released at a height h and travels around a loop-the-loop of radius R, what must h be in terms of R in order for the bead to make it to the top of the loop?

A. h=3R

B. h=2.5R

* C. h=2R

D. h=1.5R

8. Two cars collide and lock bumpers together. The final velocity of the combined cars is 0 m/s. Which of the following is conserved in the collision?

A. Mechanical energy

* B. Momentum

C. Both A and B.

D. Neither A nor B.

9. A car of mass 1000 kg traveling at 4 m/s rear ends a stationary car of mass 2000 kg. If the cars stick together, what is the final velocity of the cars? How much kinetic energy is lost in the collision (if any)? (Note: For experimental data, ask your TA. He has recently done this experiment with his own car.)(2 pts)