The 170-lb skier is schussing on a 25º slope. At the instant shown, he is moving at 40 ft/...

The 170-lb skier is schussing on a 25º slope. At the instant shown, he is moving at 40 ft/s. The kinetic coefficient of friction between his skis and the snow is μk = 0.08. If he makes no attempt to check his speed, how long does it take lot it to increase to 60 ft/s?