From conservation of momentum we note as we are considering the decay of a -meson at rest, the magnitude of the two decayed particles, the neutrino and the muon, will be equal and that they will be moving in opposite directions. Let the magnitude of momentum of either of the particles be p. Let the energy of the neutrino be and that of the muon be . Applying conservation of energy, we have

So, we have

Simplifying this algebraic equation, we find the kinetic energy of the neutrino which is equal to its energy as it has zero rest mass,

Kinetic energy of the muon will be