1. The problem statement, all variables and given/known data A proton with M0 and energy 200 MeV collides with another proton at rest. How much kinetic energy does either proton have in the inertial frame in which they collide with equal and opposite momentum 2. Relevant equations KE=1/2mv2 p=γmv λ=1/√(1-v2/c2) E=moc2γ 3. The attempt at a solution Initially I figured I would need to solve for the velocity of the particle moving towards the rest particle. I use KE=1/2mv2 and get vim0 to be 0.65c I also calculated my γ using my vi, and got 1.32 I understand that in all frames, the laws of physics hold, and as well that mass is going to be transferred from one particle to the other after the collision (energy). I am not sure how I should set up a diagram to have it make sense to me though - the wording of the problem is throwing me off a bit. My mind tells me that if one proton a hits rest proton b, some energy from proton a will be transferred in the form of mass to proton b. Proton b will then start moving in the positive direction with momentum p. Proton a will bounce back with momentum -p, but the mass will be less and the velocity higher. Am I on the right track at all? Or am I misinterpreting the question all together? Thanks!