A bullet emerges from a barrel of length 1.2m with a speed of  640 m/s. Assuming constant acceleration, the approximate time that it spends in the barrel after the gun is fired is……….ms

Given  $s=1.2m$
           $v=640m/s$
            $u=0$
From equation  $v^2-u^2=2as$
                     $640\times 640=2a\times 1.2$
                    $a=\frac{64\times 64\times {10}^2}{2.4}=\frac{8\times 64\times {10}^3}{3}$
From equation  v=u$+$at

                        $\begin{array}{l}t=\frac{v}{a}=\frac{640\times 3}{8\times 64\times {10}^3}\\ =\frac{3}{8}\times {10}^{-2}\\ =0.375\times {10}^{-2}\\ =3.75\mathrm{ms}\end{array}$