# Gravitational potential energy of skier

1. Feb 23, 2008

### kittymaniac84

1. The problem statement, all variables and given/known data

A 78.9-kg skier rides a 3150-m-long lift to the top of a mountain. The lift makes an angle of 11.9 ° with the horizontal. What is the change in the skier's gravitational potential energy?

2. Relevant equations

W=mgcos$$\theta$$(ho-hf)

3. The attempt at a solution

W=78.9*9.8*cos11.9*(0-3150)=-264,810.95J

I am confused if the angle i used was correct or should i subtract it from 90 or something. I tried that and it was still wrong. Can someone tell me what im doing wrong? is the angle used right
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Feb 23, 2008

### nicksauce

First of all, the skier is going UP the mountain. Should his gravitational potential increase or decrease?

3. Feb 23, 2008

### chocokat

Another note, although they are the same units, you are looking for gravitational potential energy, not work, so your formula isn't quite right.

GPE = mgh

So, you need to find 'h'. If the angle is 11.9˚ with the horizontal, how would you find the height?

4. Feb 23, 2008

### kittymaniac84

oh, so the height would be 3150*sin11.9= 649.54m

GPE= 78.9*9.8*649.54=502,237.3J

Is that right?

5. Feb 23, 2008

### chocokat

Assuming the skier started at height 0, then that answer looks right to me.

6. Feb 23, 2008

### kittymaniac84

that was correct..thanx!

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