Compute the force exerted on the palm of you hand by the beam from a 1.0W flashlight. (a) if your hand absorbs the light, and (b) if the light reflects from your hand. What would the mass of the particle that exerts that same force in each case would be if you hold it at earth's surface? On the problem I used E = pc to solve part (a). My lack of understanding lies in part (b). Where I am told that the momentum change is twice the amount. I do not understand. [P][/total] = [P][/1] + [P][/2] Shouldn't [P][/1] cancel with [P][/2] since the momentum of [P][/2] is moving in the opposite direction?