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Gravitational ratios

  1. Oct 10, 2006 #1
    At a certain distance above the surface of the Earth, the graviational force on an object is reduced to 18% of its value at Earth's surface. Determine this distance and express it as a multiple of Earth's radius.

    FYI the Earth's mass is 5.98x10^24 kg
    and the Earth's radius is 6.38x10^6 m

    What I did was this: Gmm/r² = (Gmm/r²)(9/50) The left side is the gravitational force on the object at the surface of the Earth and the right side is %18 of that force (radius is unkown). Since Gmm is constant in both i came up with:

    1/r² = 9/50r²
    1/6.38x10^6 = 9/50r²
    r = 1070m

    But I don't understand what they mean in by a multiple of Earth's radius. In the back of my book the answer is 1.4 Re. Is my answer wrong? Or do I just need to take it another step? Thanks for any help!
     
  2. jcsd
  3. Oct 10, 2006 #2

    arildno

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    DO NOT PUT IN THOSE MEANINGLESS FIGURES!!! :grumpy:

    Instead:
    1. What is meant by a multiple?
    In particular: In SYMBOLS, what is a multiple of the Earth's radius?
     
  4. Oct 10, 2006 #3
    I assume its a ratio...in the back of the text the answer is 1.4 Re
    (r subscript e...Radius earth) I'm not sure what it means or its significance:frown: .
     
  5. Oct 10, 2006 #4

    arildno

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    What does it mean to multiply?

    Do you think that has anything to do with the word "multiple"??
     
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