A ball rolls off the top of a staircase 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

• A

  $\mathrm{n}=\frac{2\mathrm{hu}}{{\mathrm{gb}}^2}$

• B

  $\mathrm{n}=\frac{2{\mathrm{hu}}^2}{\mathrm{gb}}$

• C

  $\mathrm{n}=\frac{2{\mathrm{hu}}^2}{{\mathrm{gb}}^2}$

• D

  $\mathrm{n}=\frac{{\mathrm{hu}}^2}{{\mathrm{gb}}^2}$