Basic potential energy question (2 Viewers)

[Glyde]

What would be the change in gravitational potential energy of a 68kg person on surface of the earth who then climbs to the peak of Mount Everest 8848metres high?

 

[Silly Sausage]

m=68kg, h=8848m

 

[InteGrand]

m=68kg, h=8848m

Should the U = -Gmm/r one be used instead here? Since h is quite significant haha.

 

[Glyde]

Should the U = -Gmm/r one be used instead here? Since h is quite significant haha.

Yeh that's what I thought :/

 

[Glyde]

It was the CHANGE in potential energy btw

 

[Silly Sausage]

Should the U = -Gmm/r one be used instead here? Since h is quite significant haha.

Was thinking of using that but cbb since I'm lazy at this point of time.

 

[InteGrand]

It was the CHANGE in potential energy btw

If the mgh formula were valid (i.e. if the altitude were low), then the Change in potential energy would indeed by mgh, since:

 

[Glyde]

If I do the -GmM/r method my solutions are different!??

 

[sy37]

If I do the -GmM/r method my solutions are different!??

-GmM/r gives you the gravitational potential energy at a specific point for the object in space. Thus if you use -GmM/r you need to use it twice (final - initial) since you are after change in GPE. Using e=mgh gives you change in gpe but assumes 'g' is constant (g is not constant because it follows an inverse relationship..look at the formula for value of g)

You will always get a different value using -gmM/r, it won't be much different for these type of questions though, but it is more accurate.