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Gravitational Potential Energy of a satellite

  1. Feb 2, 2009 #1
    Can someone help me..

    A satellite of mass 100kg revolves round the Earth in a circular orbit of radius 2R where R is the radius of the Earth. Determine the energy needed to move the satellite to a new orbit of radius 3R.

    Thanks alot.
     
  2. jcsd
  3. Feb 2, 2009 #2
    Hi Victorian91! Welcome to PF :smile:

    You have to show what you've done/tried first before we can help.
     
  4. Feb 2, 2009 #3
    Okay..
    This is how i did my solution to this problem..

    In the old orbit, Ui = - GMm/2(2R)

    In the new orbit, Uf = - GMm/2(3R)

    Energy needed U = Uf -Ui

    = GMm/ 12R

    = 5.2X10^8 J

    Is this correct?

    Or it should be just putting in 2R and 3R..

    Thanks..
     
  5. Feb 2, 2009 #4
    Why do you have the 2 in the denominator of each? I think you should have Ui = -GMm/2R and Uf = -GMm/3R. I'm curious why you thought the extra 2 came in.
     
  6. Feb 3, 2009 #5
    Yes I agree with you..

    Just that I was skeptical when my textbook included the 2(2R) and 2(3R)

    That is why I post this ..

    Could anyone know why?
     
  7. Feb 3, 2009 #6
    I have no idea why the textbook included the extra 2. Are you sure that's exactly the problem in the book?

    Also, out of curiosity, which textbook is it?
     
  8. Feb 3, 2009 #7
    Well,

    Its PRE - U Text STPM
    Physics (Volume 1 )

    Maybe a printing error..

    :confused:
     
  9. Feb 19, 2009 #8
    That is correct but without the 2* that just seems weird, when i calculated the energy required i got an answer of 1.04x10^9J..... What is the correct answer?
     
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