1. The problem statement, all variables and given/known data Show that a free electron cannot absorb a photon and conserve both energy and momentum in the process. Hence, the photoelectric process requires a bound electron. (Eisberg and Resnick 2nd Ed) 2. Relevant equations hv = E p = K / c E2 = (pc)2 + (m0c2)2 3. The attempt at a solution I've simply shown since E2 = (pc)2 + (m0c2)2, rest energy of a moving electron isn't zero and thus energy and momentum cannot be conserved. Is this argument true/suffice?