# Work Done

1. Oct 7, 2007

### Phykid

1. The problem statement, all variables and given/known data
A skier with a mass of 70kg rides a chairlift to a point of 20m higher up a ski slope.
She then Skis back down to the bottom of the chairlift.

Calculate the work done against gravity by the chairlift in carrying the skier up the slope
(Assume that g=10n/kg)

2. Relevant equations
Work Done = F x D

3. The attempt at a solution
Work done = 70 x 20
= 1400

*This is the part where I am confused.*

When we started out doing Work done, we never involved work done against another force. So Would I multiply the Work Done (1400) by 10 (kg, Gravity)?

Thanks,
Phykid

Edit - The following question: "Find the skier's speed when she reaches the bottom of the chairlift.
Ignore the effects of friction and air resistance and assume that g=10n/kg

Last edited: Oct 7, 2007
2. Oct 7, 2007

### mgb_phys

Rememebr the force is the weight of the skier in Newtons, F = m g

To get the speed simply assume that potential energy change PE = m g h
equals the kinetic energy KE = 1/2 m v^2

3. Oct 7, 2007

### Phykid

So if I am working it out against gravity, would I multiply the 14000 by 10 (gravity)?

Thanks.
Phykid