Construction worker Fred, who has a mass of 96 kg, stands on a girder. He sees a sandbag of mass 33 kg sitting on the ground, a distance 12 m below. A massless rope tied to the sandbag runs up and over a frictionless pulley connected to the girder. "Aha!", says Fred, "I'll lower myself to the ground gently by grabbing the rope. I'll fall slowly to the ground while the sandbag rises up to the girder. Brilliant!" How fast will Fred be moving when he reaches the ground? Ok. Now, I assume velocity is negative, since the man is "falling"/moving down. To find acceleration down I thought it would be Force down over the summation of weight: i.e. (9.8 m/s^2 * 96kg) / (96 + 63) = 5.9169 m/s^2 Then, I need his velocity when he reaches the ground, i.e.: V final. Vf^2 = Vi^2 + 2ad Vf^2 = 0^2 + 2 (5.9169 m/s^2)(12) Vf^2 = 142.0075 Vf = 11.9166 m/s Since the man is using the pulley to move DOWN, the position is going negative and thus velocity must be negative (I think? :( ) Vf = -11.9166 m/s The "online-homework grader" is saying my answer is wrong, can anyone tell me where I messed up and how to fix it?