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Homework Help: Satellites again

  1. Apr 3, 2005 #1
    here is another problem...
    a 650kg satellite is to be placed into synchronus orbit around Earth.
    What amount of work must be done onthe satellite to raise it into synchronous orbit?

    i did..
    W=GMm(1/r of Earth - 1/r of synchronous satellite)
    = 6.673x10^-11N m^2/kg^2 (5.98x10^6kg)(650kg)(1/6.38x10^6m - 1/4.22x10^7m)
    W = 3.442998737X10^10 J

    the right answer is 3.7x10^10 J... is ther something wrong with the significant digits?? can anyone tell me the mistake that i did?
  2. jcsd
  3. Apr 3, 2005 #2

    What kind of energy did you calculate for the satellite? Does it have any other kind when it's in orbit?
  4. Apr 3, 2005 #3
    a) the gravitational potential energy is -4.1x10^10 J
    b) the total enrgy is -3.1x10^9 J

    d) the kinetic enrgy is 3.1x10^9 J
  5. Apr 3, 2005 #4
    The kinetic energy in this case is not the same as the potential energy. The only time kinetic energy = Potential energy is when the change in kinetic energy is caused by a change in potential energy. In this case, the potential energy is always cosntant as in a circular orbit, the satelite is always the same distance from the earth.
  6. Apr 3, 2005 #5
    i get the right answer from doc al... he said that...
    change of energy = Work-Energ(total)

    therefore.. Work = Work-E
    =3.442998737X10^10 J - (-3.1x10^9 J)
    so the answer is right!!!

    thanks again for the help...
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