1. The problem statement, all variables and given/known data A collision between two particles in which kinetic energy is conserved is described as elastic. Show, using the Galilean velocity transformation equations, that if a collision is found to be elastic in one inertial reference frame, it will also be found to be elastic in all other such frames. Could this result have been predicted from the conservation of energy principle? 2. Relevant equations 3. The attempt at a solution I don't have trouble with the first part - the part I don't understand is the last question - could the result of the invariance of elastic collisions have been predicted by the conservation of energy principle? I guess I don't know enough about what the conservation of energy principle says in regard to inertial frames. According to the principle, is energy conserved only in your own frame or in all inertial frames?