A plane electromagnetic wave of wave intensity 6W/m² strikes a small mirror of area 40 cm², held perpendicular to the approaching wave. The momentum transferred by the wave to the mirror each second will be:

1.6 x 10^–10kg–m/s

$ p = \frac{2U}{c} = \frac{2S_{av} A}{c} = \frac{2\times 6\times 40\times 10^{-4}}{3\times 10^8} = 1.6\times 10^{-10} Kg/m-s$