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Ratio of planet masses

  1. Jul 11, 2011 #1
    1. The problem statement, all variables and given/known data

    The weight of an object of mass 1kg at the surface of Mars is about 4N. The radius of Mars is about half the radius of Earth. Estimate the ratio:

    mass of Mars/Mass of Earth

    2. Relevant equations

    3. The attempt at a solution

    The answer is 0.1 but I don’t see where that comes from? 1kg would be 10N on Earth but 4/10 is 0.4 not 0.1? I’m assuming the radius is important but I don’t know how.
  2. jcsd
  3. Jul 11, 2011 #2


    User Avatar

    Staff: Mentor

    Hi puzzled2, welcome to PF.

    Can you write Newton's law of gravitation for the two cases?
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