In the Compton effect, a 0.100nm photon strikes a free electron in a head-on collision and knocks it into the forward direction. The rebounding of the photon recoils it directly backward. Use conservation of (relativistic) energy and momentum to determine: a) the kinetic energy of the electron, and b) the wavelength of the recoiling photon. Assume the electron's kinetic energy is given by the non-relativistic formula. For starters, I've found the following information about the photon. Energy = 1.986*10^-15 J Momentum = 6.626*10^-24 N.S The main reason I'm having trouble with this question is because the photon recoils directly backwards and there is no angle change. I would be right otherwise, because I could use the Compton eqaution, but we never went over a question like this. I'm just not sure how to find any of the relevant information about the photon as well as the electron after the collision, like the momentum or energy transferred to the electron. I know there are a few other general formula's that I could use to determine various aspects of the photon or electron afterwards, but they involve using values relevant to the photon/electron after collision. So I'm pretty much stuck.