Elastic collisions

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Energy and momentum are conserved in elastic collisions. In the game of billiards, elastic collisions occur between balls of equal mass. However, elastic collisions can occur between objects of very different mass. This difference in mass creates different outcomes for the collisions. In each of the following demonstrations, before the collision one cart is moving and one is stationary, but the outcome of the collision depends on the masses and velocities of the carts.

For elastic collisions of bodies of equal mass (m1=m2), where one body is initially at rest, the moving body transfers all its energy and momentum to the stationary one as seen in the movie.

If the initially moving cart is more massive that the stationary cart as in the figure above, it transfers energy and momentum to the lighter cart, but keeps moving in the same direction. This is analogous to a large truck colliding with a sub-compact car. The movie demonstrates that the truck may be slowed down some, but the little car is affected much more in order to conserve momentum and energy.

When the initially moving cart is much lighter that the stationary cart as in the figure above, it bounces back and the initially stationary heavy cart moves off slowly as seen in the movie. As the stationary cart gets heavier it moves slower.

1. What is the motion of the center of mass of the two cart system for each of the demonstrations?
2. Can the movies be run backwards? Explain how that changes their description.
3. List a real life situation that is like a collision from each of the categories.