A 65 kg person is just learning how to ski. Starting from rest, the skier slides

Question

A 65 kg person is just learning how to ski. Starting from rest, the skier slides down a hill of height H = 2.5 m, and ends up moving at 5.0 m/s at the bottom. How much work did the forces of friction and air drag do on the skier? (There are no other forces but friction, air drag, and gravity.) Give your answer in Joules to three digits. Do not include the units in your answer.

Explanation / Answer

gravitational energy = P.E. = mgh =>P.E. = 65*2.5*9.8 = 1592.5 J kinetic energy = K.E = (1/2)mv2 =>K.E. = (1/2)(65)(25) = 812.5 J => The work done by friction = 1592.5 - 812.5 = 780 Answer: 780

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