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Homework Help: Need help figuring our periods of planets

  1. Sep 19, 2008 #1
    1. The problem statement, all variables and given/known data
    OK here's the question: What is the period of a planet orbiting 3 A.U. from a star 3 times as massive as the sun? And my teacher says to use keppler's 3rd law revised by newton but im completly confused by the equation and how to use it on this problem.

    2. Relevant equations
    P^2= 4*pi^2/G(m1+m2) * R^3 is the equation

    3. The attempt at a solution
    I have no idea where to even begin... please help. Suggestions?
  2. jcsd
  3. Sep 19, 2008 #2


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    Gold Member

    The 4 pi squared and G are just constants. In this question you can replace m1 and m2 by just the mass of the sun, and r is the radius of the orbit which is given as 3AU.
  4. Sep 21, 2008 #3
    Thank you!
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