1. The problem statement, all variables and given/known data the question gives me the masses and initial velocities of two balls which collide elastically and asks me to prove that it the momentum will be conserved in both a still reference frame and a moving one. 2. Relevant equations 3. The attempt at a solution i know that the momentum will be conserved in the moving frame because the final velocities will account for the change in the initial once due to the added velocity, however i don't know how to prove this without being given the final velocities.