1. The problem statement, all variables and given/known data Ball 1, with a mass of 110g and traveling at 15m/s , collides head on with ball 2, which has a mass of 350g and is initially at rest. What are the final velocities of each ball if the collision is perfectly elastic? 2. Relevant equations Conservation of momentum: m1u1 + m2u2 = m1v1 +m2v2 and energy conservation for kinetic energy: 1/2m1u1^2 + 1/2m2u2^2 = 1/2m1v1^2 + 1/2m2v2^2 3. The attempt at a solution Its really the algebra that I am stuck at, at this point. Using the momentum equation, I got v1 = (1.65kg m/s - 0.35kgv2) / 0.11kg and I know that I have to plug that into this equation: 1/2 (0.11kg) (15m/s)^2 = 1/2 (0.11kg) v1^2 + (0.175kg)v2^2 I really get lost at this point, I keep end up adding or subtracting numbers to 0. Any help would be greatly appreciated. Thank you!