1. The problem statement, all variables and given/known data Hi everyone. Hope i'm not breaking any forum rules, because i've alread wrote this one in another thread by mistake. Here is where it should be. Two balls of different mass are dropped one in top of the other, with the light one on top. After they collide with the floor (elastic collision), what is the velocity of both balls? m is the mass of the small ball M is the mass of the heavier one v is the velocity of both balls before the collision with the ground v1 and v2 are the velocities of the lighter and heavier ball respectively. 2. Relevant equations pi=pf 3. The attempt at a solution (m + M)v = mv1 + Mv2 What do i assume now? I first assumed that mv1 = -(m+M)v + Mv2 but it doesn't look right to me because v1 turns out 2v2. What am i doing wrong? Thanks in advance.