1. The problem statement, all variables and given/known data A 6.7-kg box is being lifted by means of a light rope that is threaded through a single, light, frictionless pulley that is attached to the ceiling. (a) If the box is being lifted at a constant speed of 2.0 m/s, what is the power delivered by the person pulling on the rope? Correct answer: 0.131 kW (b) If the box is lifted, at constant acceleration, from rest on the floor to a height of 1.6 m above the floor in 0.42 s, what average power is delivered by the person pulling on the rope? Correct answer: 0.713 kW 2. Relevant equations W=|F||d|cos(θ) Power = Work/Time ∑F = ma 3. The attempt at a solution For a, I've solved correctly; P=T*v = Tvcos(Θ) P=T*v (cos(0°) = 1, so I removed it) ∑F = ma a = 0 ∑F = T - W = T- (m*g) = 0 ∑F = T - (6.7kg*9.81 m/s^2) = 0 T = 65.727 N P = 65.727 N * 2.0 m/s = 131.454 W = .131454 kW for b, I'm doing something wrong; I started with using the a kinematic equation to solve for a s = V(o)t + .5at^2 1.6m/(.5*(0.42s)^2) = a = 18.14058957 m/s^2 F = ma F = 6.7kg(18.14058957 m/s^2) = 121.5419501 N Work = |F||d| W = 121.5419501 N * 1.6 m = 194.4671202 J P = Work/time P = 194.4671202 J / .42 s = 463.0169528 W = .4630169528 kW Which is obviously wrong from the correct answer that is given....any help would be greatly appreciated. Thanks in advance.