1. The problem statement, all variables and given/known data http://puu.sh/brbpb/3c7573fa32.png [Broken] 2. Relevant equations E = (mc^2 +K + mc^2 + K) P = E/c E = mc^2 3. The attempt at a solution The book says that the momentum/kinetic energy of the electron and positron produced in a pair production is so small that it can be assumed that the electron only holds rest energy. I just don't know. The question states that they have momentum, but how am I supposed to find that when I'm given so little information? All I know is that the photon has at least 1.02MeV, but how am I supposed to know how much extra energy went towards increasing the electron's momentum? Thanks.