A number of bullets are fired in all possible directions with the same initial velocity u. The maximum area of ground covered by bullets is

A bullet fired at angle 45° will fall maximum away, and all other bullets will fall with this bullet fired at 45°. 
$$\begin{gathered} {\mathrm{R}}_{\max }=\frac{{\mathrm{u}}^2}{\mathrm{g}} \\ \text{ Maximum area covered }=\mathrm{\pi }{\left({\mathrm{R}}_{\max }\right)}^2=\mathrm{\pi }\left(\frac{{\mathrm{u}}^2}{ \mathrm{g}}\right) \end{gathered}$$