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 horizontal direction =u·n=ut Initial velocity along vertical direction is 0. nh=0+12gt2∣  From t=nbv, putting t in (ii), we get  nh=12 g×nbu2   or   n=2hu2gb2