Net force experienced $$ = \frac{{{\text{Total Impulse}}}}{{{\text{Time}}\,{\text{taken}}}}$$
$$ = \frac{{m\Delta v}}{t} = 0.15 \times \frac{{20}}{{0.1}} = 30\,N$$

As we know, $$\left| a \right| = \left| {\frac{{{v^2} - {u^2}}}{{2S}}} \right| = \frac{{400}}{{50}} = 8\,m/{s^2}.$$
So force required $$ = F = ma$$
$$ = 800 \times 8 = 6400\,N$$