I am trying to desgin a little penny balista toy (built with a 3d printer). The

Question

I am trying to desgin a little penny balista toy (built with a 3d printer).

The short description is that there is a track with a mass ("hammer") that slides along it. There is a stack of pennies in a hopper at the front. The hammer goes from back to the front, slams into the penny at the end and launches it.

I had a debate with a friend about whether it would go farther if the penny started at the back and was accelerated along the full length of the track along with the hammer (a more difficult design).

My question is, all else being the same, which method would impart more energy to the penny? (my suspicion, based on those "newtons cradle" toys, is that it would be the same).

Explanation / Answer

If the mass of the penny is negligible comparing to the hammer, The speed of the hammer at the end of the track should be the same in both cases. With the collision in the first scenario, the speed of the penny should be twice of the hammer if the collision is complete elastic. But, for the second move-along scenario, the speed of the penny will be just the same as the hammer at the end of the track.

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