JEE Main 11 April 2015 Paper

A large number (n) of identical beads,each of mass m and radius r are strung on a thin smooth rigid horizontal rod of length L (L > > r) and are rest at random positions.The rod is mounted between two rigid supports (see figure).If one of the beads is now given a speed v, the average force experienced by each support after a long time is (assume all collision are elastic):