A 5MeV electron undergoes annihilation with a positron that is at rest, producing two photons. One of the photons travels in the direction of the incident electron. Calculate the energy of each photon. So the 5 MeV electron undergoes annihilation with a positron and from that 2 seperate photons are formed. The energy of both photons should equal back up to the 5 MeV correct? Also one of the photons travels back the same way the electron came but I am not clear on how to use that piece of info.