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# Assume that the right is the positive direction. A 0.099 kg marble sliding to the right at 22.5 cm/s on a frictionless surface -?

makes an elastic head-on collision with a 0.015 kg marble at rest. After the collision, the first marble continues to the right at 8.7 cm/s. The velocity of the second marble is

________ ________. Answer in m/s.

Round your answer to 2 decimal places. The second blank is for units.

### 1 Answer

- NCSLv 72 months agoFavorite Answer
Conserve momentum:

0.099kg*22.5cm/s + 0 = 0.099kg*8.7cm/s + 0.015kg*V

solves to V = 91.08 cm/s ◄

Note, however, that this collision is impossible. There is more KE after the collision then before, which isn't possible if we have simple marbles. (We'd need some sort of explosion at impact.) So if in fact you posted the wrong numbers, just plug the correct ones into the momentum equation and re-solve.

This one doesn't require much calculation if you consider that for an elastic head-on collision, the relative velocity of approach is equal to the relative velocity of separation. For the second marble, then,

V = 22.5cm/s + 8.7cm/s = 31.2 cm/s