A ball rolls off the top of a staircase with a horizontal velocity u m s^-1. If the steps are h meter high and w meter wide the ball will hit the edge of the nth step if:

• A

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

• B

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

• C

  $\mathrm{n}=\frac{2{\mathrm{u}}^2}{{\mathrm{gw}}^2\mathrm{h}}$

• D

  $\mathrm{n}=\frac{2{\mathrm{hw}}^2{\mathrm{u}}^2}{\mathrm{g}}$