A ball rolls of the top of a stair way with a horizontal velocity u m/s. If the steps are h metre high and b metre wide, the ball will hit the edge of the nth step, if

The situation is shown in fig. (1)If the ball hits the ns step, thenhorizontal distance traversed = nbvertical distance traversed = nhHere, velocity along horizontal direction = uvelocity along vertical direction = 0∴ nb=ut and nh=0+12gt2 or  t=nbu and nh=12g×nbu2∴ n=2hu2gb2