A ball rolls off the top of a staircase with a horizontal velocity u ms-1. If the steps are h metre high and b metre wide, the ball will hit the edge of the nth step, if

If the ball hits the nth step, then horizontal distance traversed = nh. Here, velocity along horizontaldirection = u.n = ut  …….(i)Initial velocity along vertical direction is 0.nh=0+12gt2   …..(ii) From t=nbv, putting t in (ii), we get nh=12g×nbu2  or  n=2hu2gb2