(c) $Given\ ,\ F = 600 - 2 \times 10^{5}\ t = 0$
$\Longrightarrow \ \ t = 3 \times 10^{- 3}\ s$
$Impulese\ \ I = \int_{0}^{t}{F \bullet dt}$
$= \int_{0}^{3 \times 10^{- 3}}{\left( 600 - 2 \times 10^{3}\ t \right)dt}$
$= \lbrack 600\ t - 10^{5}\ t^{2}\rbrack_{0}^{3 \times 10^{- 3}} = 0.9\ Ns$