1. The problem statement, all variables and given/known data An elementary particle of mass M completely absorbs a photon, after which its mass is 1.01M. a) What was the energy of the incoming photon? b) Why is that energy greater than 0.01Mc2? 2. Relevant equations E = mc2 or Δm = Δ E/c2 E = γmc2 3. The attempt at a solution The only thing I can see doing is Δm = 1.01M - M = 0.01M = E/c2 But that gives E = 0.01Mc2 , which according to part b is not the answer. How do you solve this?