Maximum deflection angle!

Classical Mechanics Level 4

A mass \(M\) collides elastically with a stationary mass \(m\). If \((M < m)\), then it is possible for \(M\) to bounce directly backwards. However, if \((M > m)\), then there is a maximum angle of deflection of \(M\). Find the correct relation between \(\theta , m, M\).

(\(\theta\) is the maximum angle of deflection.)