[QUE/EPP-01010]

The decay of a massive particle \(A\) into two particles \(B,C\) \begin{equation} A \longrightarrow B  +  C \end{equation} is not possible  when \(M_A < M_B + M_C\).

1. Show this by applying momentum energy conservation in the rest frame of particle \(A\).
2. Why does your argument not remain valid for the case when mass of particle \(A\) goes to zero.