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Homework Help: Another Planetary Mechanics Question

  1. May 29, 2007 #1
    1. The problem statement, all variables and given/known data
    A NASA spaceship is orbiting the moon at an altitude of 111 km. How long does it take the ship to make one orbit around the moon?

    This was a question on the test I had today, just wondering if I'm out to lunch or not. So he gave us all the info on the moon on an overhead. I used the mass of the moon 7.36*10^22 kg and the radius 1,737,000m added to the altitude.

    2. Relevant equations
    I used the equation mp=4π²R³/GT²

    3. The attempt at a solution
    So I plugged in 7.36*10^22=4π²(1848000)³/6.67*10¯¹¹(T²) and solved for t.

    I got with sig figs 7120 seconds or something like that on the test. His numbers might have been slightly different. Did I do this completely wrong?
    Last edited: May 29, 2007
  2. jcsd
  3. May 30, 2007 #2
    I'm not familiar with the equation that you are using, that is to say that it must be derived from a couple of other equations, but it could be correct.

    I would have used potential energy to find the angular velocity, and then the period. Just approximating in my mind, I think you are right or close to right.
  4. May 30, 2007 #3
    Alright well thank you for your help. We have not learned about potential energy yet but if you think my answer is in the ballmark, that makes me worry a lot less!
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