Gravitational Potential Energy - Orbits

  • Thread starter Nicolaus
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  • #1
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Homework Statement


A satellite is in a circular orbit 655km above Earth's surface. Determine the magnitude of the gravitational acceleration at this height.


Homework Equations


Eg=mgh
Eg=-GMm/r


The Attempt at a Solution


Would I just set the aforementioned eqations equal to each other and re-arrange to solve for g? I would also have to solve for the change in Eg, as well, right?
 

Answers and Replies

  • #2
Doc Al
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Would I just set the aforementioned eqations equal to each other and re-arrange to solve for g?
No. Instead of potential energy, think in terms of forces and acceleration. What is the gravitational force on the satellite. (Tip: Don't be so quick to plug in numbers.)
 
  • #3
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Well, it's also experiencing a centripetal force. If we set Fc=Fg, we can get the velocity of the orbit, but, other than that, I'm not sure how to do this without the mass of the sat.
 
  • #4
Doc Al
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Well, it's also experiencing a centripetal force. If we set Fc=Fg, we can get the velocity of the orbit, but, other than that, I'm not sure how to do this without the mass of the sat.
You won't need the mass--just call it 'm'. When you calculate the acceleration, it will drop out.

What is Newton's law of Universal Gravity?
 
  • #5
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Got it - I was overthinking a rather simple question..., thanks.
 
  • #6
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Also, E=mgh only works for constant gravitational fields. i.e. at the surface of a very large mass (like the Earth).
 

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