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Gravitational Potential Energy - Orbits

  1. Oct 20, 2012 #1
    1. The problem statement, all variables and given/known data
    A satellite is in a circular orbit 655km above Earth's surface. Determine the magnitude of the gravitational acceleration at this height.


    2. Relevant equations
    Eg=mgh
    Eg=-GMm/r


    3. 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?
     
  2. jcsd
  3. Oct 20, 2012 #2

    Doc Al

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    Staff: Mentor

    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.)
     
  4. Oct 20, 2012 #3
    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.
     
  5. Oct 20, 2012 #4

    Doc Al

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    Staff: Mentor

    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?
     
  6. Oct 20, 2012 #5
    Got it - I was overthinking a rather simple question..., thanks.
     
  7. Oct 20, 2012 #6
    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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