1. The problem statement, all variables and given/known data A proton has total energy 2GeV and is travelling along the x-axis. A photon with energy 50MeV travels at an angle of 45 degrees to this axis. What is the total energy and momentum of the system? 2. Relevant equations Non-really 3. The attempt at a solution Total E = 2Gev + 50 MeV = 2.05GeV yes? I don't need to take any directions into account here do I? Then px = p(proton) + px(photon), and py = py(photon) yes?