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Homework Help: Universal gravitation - radius?

  1. Apr 2, 2010 #1
    Using F = G * (m1*m2)/(r2)

    We know that

    G = 6.6673x10-11 N*m2/kg2
    m1(earth) = 6x1024 kg
    m2(moon) = 7.4x1022 kg
    the earth and moon are an average of 3.9x108m apart

    would r2 be [3.9x108]2 or [3.9x108 / 2]2?

  2. jcsd
  3. Apr 2, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Why would you divide the distance in half?
  4. Apr 2, 2010 #3
    Here we are using radius...........!
    So, the first one is correct.

    Here the distance between the two bodies mean the distances from their centres.
    So, definitely, they are mentioning the radius
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