A bullet emerges from a barrel of length 1.2 m with a speed of $640 {\mathrm{ms}}^{-1}$. Assuming constant acceleration, the approximate time that it spends in the barrel after the gun is fired, is

Given, s = 1.2 m, v = $640 {\mathrm{ms}}^{-1}$

                   $\mathrm{a} =?; \mathrm{u} = 0; \mathrm{t}=?$

                $2as = v^2-u^2$
$\Rightarrow$      2a x 1. 2 = 640 x 640

$\Rightarrow$            $\mathrm{a} = \frac{8 \mathrm{x} 64 \mathrm{x} 1000}{3} m/s$

                        v = u + at

$\Rightarrow$                   $t=\frac{v}{a}=\frac{640\times 3}{8\times 64\times 100} s =3.75\times {10}^{-3} \mathrm{s}\approx 4 \mathrm{ms}$