A block slides down a frictionless plane that makes an angle of $30$ with the horizontal. The acceleration of the block is

$8\mathrm{.}49\frac{m}{s^2}$

$4\mathrm{.}90\frac{m}{s^2}$

$5\mathrm{.}66\frac{m}{s^2}$

$9\mathrm{.}80\frac{m}{s^2}$

$0\frac{m}{s^2}$