1. The problem statement, all variables and given/known data A body X moving with a velocity v makes an elastic collision with a stationary body Y of equal mass on a smooth horizontal surface. Which statement gives the velocities of the two bodies after the collision? (multiple choice question) 3. The attempt at a solution The answer according to the mark scheme is velocity of X = 0 velocity of Y = v So I can't understand how this is worked out. But this as far as I got: MUx+MUy = MVx + MVy Ux +Uy = Vx +Vy Ux = Vx + Vy How do you know that Vx is 0 and Vy is V (or Ux)?