Explanation

(d) According to Newton’s second law of motion,
$F = \frac{\mathrm{\Delta}p}{\mathrm{\Delta}t}$
$Also,\ \ F = ma$
$\therefore\ \ \ ma = \frac{p_{2} - p_{1}}{\mathrm{\Delta}t}$
$or\ \ \ a = \frac{m_{2} - \left( - {mv}_{1} \right)}{m\mathrm{\Delta}t}$
$or\ \ a = \frac{v_{2} + v_{1}}{\mathrm{\Delta}t}$
$\therefore\ \ a = \frac{\sqrt{2 \times 10 \times 20} + \sqrt{2 \times 10 \times 5}}{0.02}$
$or\ \ \ a = \frac{20 + 10}{0.02} = 1500\ {ms}^{- 2}$