A coin is placed on a horizontal platform which under goes vertical simple harmonic motion of angular frequency $\mathrm{\omega }$). The amplitude of oscillation is gradually increased. The coin will leave contact with the platform for the first time:

• A

  for an amplitude of $\frac{{\mathrm{g}}^2}{{\mathrm{\omega }}^2}$

• B

  at the highest position of the platform

• C

  at the mean position of the platform

• D

  for an amplitude of $\frac{\mathrm{g}}{{\mathrm{\omega }}^2}$