I have a problem, I'm trying to work out this simple equation and I'm confusing myself. This is the question: a white snooker ball hits a stationary red ball elastically at speed of 50cm/second, and both move off at different velocitys. if the balls are the same mass(50g) and the final velocity of the white ball is 20 cm/seconds, what is the final speed of the red ball. If I use the conservation of momentum equation or equal the KE on both sides of the equation I get different answers? Do i assume that the white balls velocity will be positive on the left side of the equation and negative on the right because the question specifies it's moving in 'different velocities'. Then if I use ½mv² = ½mv² I get a different answer. Can someone explain what I am doing wrong? Thanks!