Posted by **ray** on Monday, May 24, 2010 at 10:11am.

4. Two masses of 3 kg and 5 kg collide head-on, the former moving to the right with the speed 5 m/s and the latter moving to the left with the speed 3 m/s.After collision they stick together. What amount of mechanical energy is lost?

5. A cylinder with a uniform density is rolling over a plane. What fraction of its kinetic energy is rotational kinetic energy?

- physics -
**drwls**, Monday, May 24, 2010 at 11:26am
4. Their momenta cancel and the stuck-together mass won't move, because

5x3 - 3x5 = 0.

All mechanical energy is lost.

5. Compare (1/2) I w^2 (the rotational KE) with the sum of (1/2) Iw^2 and (1/2) M V^2.

Note that I = (1/2) M R^2 (for solid cylinders) and

V = R w (for rolling objects). You should end up with a fraction independent of M, R and w.

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