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?

A.) We use the famous equation proposed by Albert Einstein written below:

E = Δmc²

where

E is the energy of the photon

Δm is the mass defect, or the difference of the mass before and after the reaction

c is the speed of light equal to 3*10⁸ m/s

Substituting the value:

E = (1.01m - m) * (3*10⁸ m/s) = 0.01mc² = 3*10⁶ Joules

b) The actual energy may be even greater than 3*10⁶ Joules because some of the energy may have been dissipated. Not all of the energy will be absorbed by the photon. Some energy would be dissipated to the surroundings.