Work-energy theorem and resistive forces

AI Thread Summary
The discussion revolves around applying the work-energy theorem to a skier's descent from a height of 250m, with an intermediate hill at 100m. The skier's speeds at the top and bottom of the hill were calculated to be 54m/s and 70m/s, respectively, assuming no resistive forces. For the third part, the focus shifts to determining the work done by resistive forces when the skier reaches the bottom with a speed of 28m/s. The solution involves calculating the difference between the expected and actual kinetic energy to find the mechanical energy lost. This approach effectively quantifies the impact of friction and drag on the skier's motion.
RedDanger
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Homework Statement


A skier slides down a hill, starting from rest at a height of 250m above the bottom of the hill. She skis over an intermediate hill, whose height is 100m above the bottom of the hill. If resistive forces are neglected, what is the speed of the skier a) at the top of the intermediate hill, b) at the bottom of the hill? c) Suppose the skier reaches the bottom of the hill with a speed of 28m/s. Assuming that the skier, including equipment, has a mass of 85Kg, how much work was done by the resistive forces of friction and drag?


Homework Equations


KEi + PEi = KEf + PEf


The Attempt at a Solution


Parts A and B I don't have trouble with, as they are simply applications of the work-energy theorem. For part A I got 54m/s, and part B I got 70m/s, but part C I have no idea how to approach.
 
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Hi RedDanger! :smile:
RedDanger said:
… c) Suppose the skier reaches the bottom of the hill with a speed of 28m/s. Assuming that the skier, including equipment, has a mass of 85Kg, how much work was done by the resistive forces of friction and drag?

Use the work-energy theorem: work done = loss of mechanical energy.

In other words, subtract the actual final KE from the expected final KE … that gives you the mechanical energy lost. :wink:
 

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