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Homework Help: Gravitational problem

  1. Mar 11, 2009 #1
    1. The problem statement, all variables and given/known data

    The mass of the earth is 5.98*10^24 kg and its radius is 6370 km. The radius of the moon is 1738 km. The acceleration of gravity at the surface of the moon is 1.62 m/s^2. What is the ratio of the average density of the moon to that of the earth ?

    2. Relevant equations

    New's law of gravity: F= G*m1*m2/r^2

    3. The attempt at a solution

    I understand that I need to find mass of the moon to get its density. How should I calculate the mass of the moon ??
  2. jcsd
  3. Mar 11, 2009 #2
    Assume a 1 kg test mass and write a statement about what is true at the surface of the earth and a similar statement for the same 1 kg mass at the surface of the moon.
  4. Mar 11, 2009 #3
    On the earth it will have the weight of 9.81 N and on the moon its weight gonna be 1.62 N. Is that what you are talking about ?
  5. Mar 11, 2009 #4
    Can I use Newton's Law of Gravity here ? But I don't know either F or r and one of the m though
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