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Homework Help: Mass of the moon

  1. Nov 13, 2008 #1
    1. The problem statement, all variables and given/known data

    Before landing men on the moon, Apollo 11 space vehicle was put into orbit about the moon. The mass of the vehicle was 9979kg and the period of the orbit was 119 min. The maximum and minimum distances from the center of the moon were 1861 km and 1838km . Assuming the moon to be a uniform spherical body, what is the mass of the moon according to these data?

    2. Relevant equations

    elliptic equation?

    3. The attempt at a solution

    I tried using the kepler's law and Gravitational equation.. It seems I can't get the mass of the moon. Anyone can help me through?

  2. jcsd
  3. Nov 13, 2008 #2


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    Period, distance and mass will suggest Newton's version of Keplers's third law. You will have to work out what the semi major axis is though.
  4. Nov 14, 2008 #3
    is the semi major axis the radius for the r^3 in the kepler's thrid law? I use the (1861+1838)/2 is correct that this is the value for r? 1849.5?

    thank for replying..
    Last edited: Nov 14, 2008
  5. Nov 14, 2008 #4


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    Yes Kepler's 3rd is based on the semi major axis. You have correctly worked it out.
  6. Nov 14, 2008 #5
    thanks then I think I got of correct d.. Thanks..
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