Explanation

(a) Applying principle of conservation of linear momentum, velocity of the system $(v)$ is
$m_{1}v_{1} = \left( m_{1} + m_{2} \right)V, \Rightarrow V = \frac{m_{1}v_{1}}{m_{1} + m_{2}} = \frac{50 \times 10}{(50 + 950)} = \frac{1}{2}ms^{- 1}$
Initial KE, $E_{1} = \frac{1}{2}m_{1}v_{1}^{2} = \frac{1}{2} \times \left( \frac{50}{1000} \right) \times 10^{2} = 2.5\ J$
Final KE, $E^{2} = \frac{1}{2}\left( m^{1} + m^{2} \right)v^{2}$
$= \frac{1}{2}\frac{(50 + 950)}{1000} \times \frac{1}{2} = 0125\ J$
Percentage loss is KE
$\frac{E_{1} - E_{2}}{E_{1}} \times 100 = \frac{2.5 - 0.125}{2.5} = 95\%$