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Homework Help: Need help-Energy of satellite

  1. Nov 26, 2007 #1
    1. The problem statement, all variables and given/known data
    msatellite = 6000 kg ;
    Mearth = 5:98 £ 1024 kg ;
    Rearth = 6:37 £ 106 m; and
    G = 6:67259 £ 10¡11 Nm2=kg2 :
    The radius of the satellite around the center
    of the Earth is r =13/2R.
    Hint: You may Find it useful to take into account that the gravitational force is a conservative force.
    Hint: The universal gravitational force law
    is F= GMm/r^2.

    Caution: Neglect the rotational kinetic energy due to the Earth's rotation.
    Find the energy required to launch a satellite from Earth into the circular orbit at the
    specified radius r =13/2R. Answer in units of J.

    2. Relevant equations
    F = GMm/r^2.

    U(gravitational) = GMm/r
    kinetic energy (translational) = 1/2mV^2 = (1/2GMm)/r

    3. The attempt at a solution

    Total energy = Kinetic + Ug = 0.5GMm/r - GMm/r = -2.8911e10 J
    but it is wrong
    please help
  2. jcsd
  3. Nov 26, 2007 #2
    maybe this will help as well

  4. Nov 26, 2007 #3
    i realized that for work = F*D, D is not r but r-R,earth because its launched from the surface of the earth, but i'm still getting a wrong answer
    please guys, i really could use some help
  5. Nov 26, 2007 #4
    okay, total energy should be K - Ug = .5GMm/r - GMm/r^2 but my answer is still wrong
    (i'm getting 2.8911e10)
  6. Nov 26, 2007 #5
    nvr mind, got the answer
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