(a) The total energy of a particle is
Convert this to electron-volts using the appropriate conversion factor which is
The total energy of the muon is 243 MeV. This should be greater than the rest energy of the muon, which is
The rest energy of the muon is 106 MeV. It therefore makes sense that the total energy of the muon (which is the sum of its kinetic energy and rest energy) is greater (243 MeV) than its rest energy. This gives us confidence in our answer.
(b) To find the muon's kinetic energy, write the total energy of the particle as the sum of the muon's rest energy and kinetic energy. Substitute the total energy and rest energy, and solve for the kinetic energy.
The kinetic energy is the difference between the total energy and rest energy and comes out to 137 MeV which is .