Gravitational Potential energy

  • Thread starter fcb
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  • #1
fcb
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Homework Statement


A satellite of the mass 500kg is boosted from an orbit of altitude 10,000 km to one of altitude 20,000km. Given that the diameter of the earth is 12,756km, its mass as 5.97x1024. calculate the change of GPE of the satellite

Homework Equations


Ep=-Gm1m2/r + altitude


The Attempt at a Solution


Ep=6.672x10-11x500x5.97x1024/(0.5x12756000m) + altitude

Am i wrong? I dont know how to do this.
 

Answers and Replies

  • #2
1,860
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What is altitude and why do you have it there? Use V=-Gm1m2/r where V represents the gravitational potential energy and r is the distance between the two objects.

For you:
V2-V1=??
 
  • #3
fcb
50
1
What is altitude and why do you have it there? Use V=-Gm1m2/r where V represents the gravitational potential energy and r is the distance between the two objects.

For you:
V2-V1=??

Well its probably wrong, But inst it supposed to be there because its a change in altitude?

Can you give me a heads up on how to do it?
 
  • #4
Changes in potential gravitational energy over a change in height are determined only by the initial and final heights, and you've got both. Just compute U (or V, however you want to call it) at height 1 and then compute U at height 2, and substract. Hint: you gotta consider gravity is acting from Earth's center.
 
  • #5
71
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this is the expression for potential energy close to earth : mgr

m = mass
g = gravity
r = height (alititude)

you are simply replacing mg with a more general expression for the forces of gravity[tex]\frac{Gm1m2}{r^{2}}[/tex]*r

this expression gives you potential energy
 
  • #6
fcb
50
1
Please, just this once. The answer in the back of the book could be wrong, but I can't seem to get the right answer
 
  • #7
492
2
You must make sure you're taking into account the radius from the center of the Earth as well. When you model force fields, you model the object exerting that force as a particle. Have you done this? Also it might help to show what you've been trying.
 

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