Physics 213 Test 3 PPAM (Problems Priced as marked)Nov. 17, 1998

Warm-ups, 5 points each.

1. What is the law of conservation of energy?

2. What is the work-energy theorem?

3. Define power.

4. What is the law of conservation of momentum?

5. Under what conditions is kinetic energy conserved in a collision?

6. Define impulse and give 2 equations for it. ( I = _________, I = ________)

7. What must always be the positive direction in a circular motion problem and why?

8. What is the direction of force on an object that is moving in a circular path?

9. What conditions are necessary for ?

Applications: 10 points each

10. Superman stands in front of a gunman firing an automatic weapon. The gun fires 40 g bullets at a speed of 800 m/s. If the gun fires 200 bullets per minute, and they bounce off superman in a perfectly elastic collision and go back from whence they cometh, what is the force on superman?

11. A 5 kg block is set into motion up an inclined plane with an initial speed of 20 m/s. The block comes to rest after traveling 12 m up the incline, which is inclined at an angle of 37^o with the horizontal.

Find the coefficient of kinetic friction between the block and the surface in the figure.

12. Definitions: Aft thrust engines propel a craft forward, forward thrust engines propel a craft backwards.

A 10⁴ kg space ship is moving forward at 600 m/s. A 5 x 10⁴ W forward thrust engine is employed for 30 seconds used to slow down the space ship.

a. What is the final velocity of the space ship?

b. What was the total impulse delivered to the space craft ?

c. What is the average force produced by the engine ?

13. A 60 kg kid on a skateboard is moving to the east at 30 m/s. He is holding his 30 kg cat . If he hurls the cat eastward at a speed of 20 m/s relative to the ground, what will be the kid on the skateboard's final velocity?

14.A 140 kg astronaut is standing on the extreme edge of a stationary 1000 kg space platform. He walks at a constant speed of 5 m/s, with respect to the platform, toward the other edge of the platform. (He wears special magnetic shoes which allow him to walk along the metal platform.) As he walks, the platform moves through space. Find the platform's velocity relative to the fixed stars.

Bonus Problem #1. 5 points

Bonus Problem #2 10 points

A child's toy consist of a piece of plastic attached to a spring (Figure below). The spring is compressed 2.0 cm, and the toy is released. If the mass of the toy is 100 g and it rises to a maximum height of 60 cm. It is again compressed 2 cm and released. This time, just as it leaves the spring, the 40 g plastic separates from the 60 g base. Estimate how high the mushroom shaped plastic rises . Hint: Since you'll be finding velocity at the instant of separation, you can ignore the force of gravity acting on the system, and assume you have an isolated system at that moment.