Light with an energy flux of 16W/cm2  falls on a non reflecting surface at normal incidence. If the surface has an area of 20 cm2  , find the average force exerted on the surface during a 30 minute time span.

The total energy falling on the surface isU = 16×20×30×605.76×105J        The total momentum delivered (for complete absorption) isp = uc = 5.76×1053×1085.763×10−3= 1.92×10−3The average force exerted=pt = 1.92×10−30.18×104 = 10.66×10−7                                                     =1.06×10−6