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Homework Help: Newton's version of kepler's law

  1. Feb 27, 2005 #1
    Use Newton's version of Kepler's third law to find the mass of Earth. The moon is 3.9*10^(8) m away from Earth, and the moon has a period of 27.33 days.

    I just have trouble with using the correct units...thanks for any help!
  2. jcsd
  3. Feb 27, 2005 #2

    James R

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    Convert days to seconds, and your data will be in standard SI units.
  4. Mar 28, 2005 #3

    Andrew Mason

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    [tex]M_m\omega^2R = \frac{GM_eM_m}{R^2}[/tex]

    [tex]M_e = \frac{4\pi^2R^3}{GT^2}[/tex]

    T is the period in seconds. R is in metres.

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