1. The problem statement, all variables and given/known data Two elastic balls of mass m1 and m2 are placed on top of each other with a small gap between them and then dropped onto the ground. What is ratio m1/m2, for which the upper ball m1 ultimately receives the largest fraction of the total energy? (m1<m2) 2. Relevant equations 3. The attempt at a solution At the instant when lower ball(m2) hit the ground, both balls will have the same velocity u1. And when the lower ball bounces up, it will have a velocity of -u1. However, the problem is that there is a gap between the two balls, and if I introduce another variable h, I don't think this variable can be eliminated at the end to give the answer m1/m2 = 1/3.