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Homework Help: Gravitational Potential Energy of the earth

  1. Mar 23, 2010 #1
    1. The problem statement, all variables and given/known data

    How high above the surface of the Earth must a mass be located so its gravitational potential energy is only 17.00% of its value on the surface?


    2. Relevant equations

    PEg=(-GMm)/r, PElocal= mgy where y is height the object can fall

    3. The attempt at a solution

    I've tried a couple of different things but all my variables cancel out.

    (-GMm)/r1=0.17((-GMm)/r2

    r1/0.17=r2 If I randomly set r1 to be 1 r2= 5.88235 but that doesn't make sense because if you raise an object by 5m it would have a greater PEg

    Any suggestions on where to go?
    Thanks!!
     
  2. jcsd
  3. Mar 23, 2010 #2

    tiny-tim

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    Science Advisor
    Homework Helper

    Welcome to PF!

    Hi kt102188! Welcome to PF! :smile:
    But the radius of the Earth is a lot larger than 1m. :confused:

    (and remember, the question assumes that the PE at ∞ is zero :wink:)
     
  4. Mar 23, 2010 #3
    Thank you! I was totally thinking of this wrong. Actually using the radius of earth got the right answer.
     
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