91. A 72-kg water skier is being accelerated by a ski boat on a flat ("glassy") lake. The coefficient of kinetic friction between the skier's skis and the water surface is HK = 0.25 (Fig. 4-74 0). (a) What is the skier's acceleration if the rope pulling the skier behind the boat applies a horizontal tension force of magnitude FT = 240 N to the skier (0 = 0)? (b) What is the skier's horizontal acceleration if the rope pulling the skier exerts a force of FT = 240 N on the skier at an upward angle 0 = 120? (c) Explain why the skier's acceleration in part (b) is greater than that in part (a). FT = 240 N HK = 0.25