(c) Loss of kinetic energy =$\frac{1}{2}\ \frac{m_{1}m_{2}}{m_{1} + m_{2}}\left( v_{1} - v_{2} \right)^{2}$
$= \frac{1}{2} \times \frac{M \times M}{M + M}\left( V_{1} - V_{2} \right)^{2}$
$= \frac{M \bullet M}{2(2M)}\left( V_{1} - V_{2} \right)^{2}$
=$\frac{M}{4}(V_{1} - V_{2})$