A rifle shoots a bullet with a muzzle velocity of 400 ms^-1 at a small target 400 m away. The height above the target at which the bullet must be aimed to hit the target is (g = 10 ms^-2).

Time taken by bullet to reach the target is
$$\begin{gathered} \frac{\text{ Distance }}{\text{ velocity }}=\frac{\text{ Distance }}{\mathrm{ucos}\theta } [\text{ As }\theta \text{ is very small, }\cos \theta =1\text{ ]} \\ \text{ Time }=\frac{\text{ Distance }}{\mathrm{u}}=\frac{400}{400}=1 \mathrm{s} \\ \mathrm{Vertical} \mathrm{deflection} \mathrm{of} \mathrm{bullet} \mathrm{is} \\ =\frac{1}{2}{\mathrm{gt}}^2=\frac{1}{2}\times 10\times (1{)}^2=5 \mathrm{m} \end{gathered}$$