**1. The problem statement, all variables and given/known data**

A nucleus of mass m initially at rest absorbs a gamma ray (photon) and is excited to a higher energy state such that its mass is now 1.01 m.

Find the energy of the incoming photon needed to carry out this excitation.

**2. Relevant equations**

[itex]m^{2} = E^{2}-P^{2}[/itex] possibly

[itex]E_{sys}= KE+E_{o}+E_{\gamma}[/itex]

**3. The attempt at a solution**

Equating energy before and after.

[itex]m+E_{\gamma}=1.01m+KE[/itex]

[itex]E_{\gamma}=.01m+KE[/itex]

Is there a way to find the exact energy required? I think it may have something to do with the momentum but they do not give any info about the motion of the final particle.

http://ift.tt/1goJ92i