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Homework Help: Using Kepler's Third Law to find mass

  1. Jan 31, 2015 #1
    1. The problem statement, all variables and given/known data
    The fictional planet Snazbort has a fictional moon Pingdol. Pingdol has an orbital period of 7.68 days and a semimajor axis of 92.53×109. Use Kepler's Third Law to estimate the mass of Snazbort.

    2. Relevant equations

    where 2a is the length of major axis
    T is the time required for it to travel once around its elliptical orbit
    G is gravitational constant
    M is mass

    3. The attempt at a solution
    I've tried plugging in the numbers and I can't seem to figure out how I'm supposed to enter them. I'm also not entirely sure how I even get G. The G I used is from another question.

    If it helps at all, the screenshot is here along with my "best" attempt.

    EDIT: I got the answer. I was supposed to change T into seconds -_-
  2. jcsd
  3. Jan 31, 2015 #2


    Staff: Mentor

    Is that semimajor axis supposed to be 92.53 X 109? What are the units?

    It's important to keep track of the units, which maybe you've already found out with the days vs. seconds units in T.
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