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Homework Help: Gravitation and Circular Orbits

  1. Jan 16, 2008 #1
    Just a question about gravitation equations:

    Neglecting Earth's rotation, show that the energy needed to launch a satellite of mass m into circular orbit at altitude h is equal to:

    [tex](\frac {GMm}{R})(\frac{R+2h}{2(R+h)})[/tex]

    Where R = the radius of the Earth and M = the mass of the Earth.

    I've tried subbing in r=h+R and it hasn't given me much help.

    Any help would be truly appreciated! Thanks all.
  2. jcsd
  3. Jan 16, 2008 #2
    Try expanding the equation and see what you get. (HINT: think [tex]W=-\Delta U_g[/tex])
  4. Jan 16, 2008 #3
    "W" as in work? or what variable?
  5. Jan 16, 2008 #4
  6. Jan 17, 2008 #5

    Shooting Star

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    What is the force that makes a body go round in a circle? What is supplying that force here? You have to equate the two.
  7. Jan 17, 2008 #6

    Shooting Star

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    Some addition which I didn't bother to mention:

    Energy reqd = (PE + KE) in orbit - PE on surface of earth. You have to use the previous concept anyway.
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