1. The problem statement, all variables and given/known data A 110 g ball moving to the right at 4.0 m/s catches up and collides with a 400 g ball that is moving to the right at 1.2 m/s. If the collision is perfectly elastic, what is the speed of the 110 g ball after the collision? 2. Relevant equations KEi=KEf 1/2m1v1i^2 + 1/2m2v2i = 1/2m1v1f^2 + 1/2m2v2f^2 3. The attempt at a solution Tried plugging it in but I don't really understand the concept so I am let with 2 final velocity. Please help. 110g < 400g so 110g should move left and 400g should move right, so does that make v2f=0?