Motion In A Plane

A ball rolls off the top of a stairway with horizontal velocity \(u\). The steps are \(0.1 \mathrm{~m}\) high and \(0.1 \mathrm{~m}\) wide. The minimum velocity \(u\) with which that ball just hits the step 5 of the stairway will be \(\sqrt{x} \mathrm{~ms}^{-1}\) where \(x=\) __________ [use \(\mathrm{g}=10 \mathrm{~m} / \mathrm{s}^2\) ].