# Potential energy problem

[SOLVED] Potential energy problem

A man that has a mass of 80.0 kg, wearing a backpack with a mass of 20.0 kg, climes 8848 m to the top of Mount Everest. What is his potential energy?

The only one I know of is PE=mgh

I added the masses, then plugged it into the equation, but I didn't get the answer.

Edit:It was already in meters. Sorry.

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Kurdt
Staff Emeritus
Gold Member
Did you convert the height in feet to meters?

Sorry, it was in meters already. I apparently can't type well today.

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Kurdt
Staff Emeritus
Gold Member
The problem is that equation only holds for short distances above the Earths surface since g depends on the height above the Earth. Have you seen any other formula for gravitational potential energy?

Tom Mattson
Staff Emeritus
Gold Member
The problem is that equation only holds for short distances above the Earths surface since g depends on the height above the Earth. Have you seen any other formula for gravitational potential energy?

Kurdt, 8848 m is a short distance above the surface of the Earth, so that is definitely not the problem.

Twilit_Truth needs to show some work if we are to figure out what the real problem is. I'm guessing he's either making a calculational error, or doing something silly like using 32 for g, when everything is in mks units. Or possibly it's more subtle. Perhaps he is using a different datum than the answer key is using. IOW, perhaps he is setting V=0 at the surface of the Earth, while the author of the book sets V=0 at the center of the Earth or at infinity.

Twilit_Truth: Let's see how you're doing this.

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Kurdt
Staff Emeritus
Gold Member
Kurdt, 8848 m is a short distance above the surface of the Earth, so that is definitely not the problem.

haha sorry. Long time since I've done one of these. Guess I was jumping too far ahead on tracking the problem.

Ok, I'll try to show you what I did. Just so you know, this is a multiple choice question.

First off, I combined the masses of the climber and the pack, resulting in a total mass of 100. kg. Then, I multiplied it by 9.81, which is the only value that I know of for g when on the Earth. This came to 981 N. Finally, I multiplied this by the height, which is 8848 m, and got 8679888 J.

The problem is, the answers are:

A) 6.94E6 J
B) 4.16E6 J
C) 2.47E6 J
D) 1.00E6 J

I don't know where I went wrong. I was absent while they taught this, so I probably messed up somewhere. Thank you both for your time.

hage567
Homework Helper
Why are there 4 answers? Is this question supposed to be part A,B,C or D?

It's a multiple choice question. Only one answer is right out of those four.

hage567
Homework Helper
It's a multiple choice question. Only one answer is right out of those four.

Oh I get it.

Anyway, I believe this is somewhat of a trick question. The question asks what is *HIS* potential energy.