Velocity and Center of mass question??? 1. The problem statement, all variables and given/known data Having some issues with this one. "Ball A has a mass of .200kg and a velocity of 1.50 m/s. Ball B has a mass of .300kg and a celocity of -0.400 m/s. The balls meet in a head on collision. After the collision, the velocity of ball A is -0.780 m/s. A) Assuming that the two balls form an isolated system, determine whether or not this was an elastic collision. and B) (Mainly this one) - Find the velocity of the centre of mass of the system, before and after the collision. ???? 2. Relevant equations 3. The attempt at a solution How do you find the velocity of the centre of mass of a system?? Any help would be great!