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Homework Help: HW Question, very simple. mass/gravity

  1. Feb 4, 2008 #1
    If a planet is 1/2 of earth, gravitational is the same of earth, what does that tell you about the mass?
  2. jcsd
  3. Feb 4, 2008 #2


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    half the size?

    anyhow...What is mass affected by?
  4. Feb 4, 2008 #3
    yes, half the size. Nothing, just trying to find out if the mass of the planets is 2 or 4 times larger/smaller than earth.

    basically if a planet is half the size of the earth, and gravitation is the same as earth, what would the planets mass have to be? 2 or 4 times larger than earth?
    Last edited: Feb 4, 2008
  5. Mar 21, 2009 #4

    If acceleration due to gravity is equal for both the Earth and another planet, then,

    Gme / re2 = Gmp / rp2.
    ==> me = (re / rp)2 mp
    ==> me = (2rp / rp)2 (given re = 2rp)
    ==> me = 4mp


    Rich B.
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