A beam of light of intensity $1000\ \text{W/m}^2$ falls on a flat, perfectly reflecting surface of area $2\ \text{m}^2$. The beam makes an angle of $60^\circ$ with the normal to the surface. Taking $c = 3\times10^8\ \text{m/s}$, the force exerted by the light on the surface, along its normal, is closest to