Work-energy theorem and resistive forces

[RedDanger]

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.

 

[tiny-tim]

Hi RedDanger!

… 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.