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Homework Help: Newton's law of gravitational attraction help?

  1. Mar 16, 2008 #1
    [SOLVED] Newton's law of gravitational attraction help?

    1. The problem statement, all variables and given/known data
    M1 is a spherical mass (38.6 kg) at the origin. M2 is also a spherical mass (10.3 kg) and is located on the x-axis at x = 61.2 m. At what value of x would a third mass with a 15.0 kg mass experience no net gravitational force due to M1 and M2?

    2. Relevant equations

    3. The attempt at a solution
    The force of m1 on m3 and m2 on m3 should be equal, so
    Gm1m3/r1^2 := Gm2m3/r2^2

    G and m3 are constant, so rearrange and get

    sqrt (m1/m2) = r1/r2

    not sure what to do here, should i just multiply this ratio by the distance 61.2m?
  2. jcsd
  3. Mar 16, 2008 #2
    But what are [tex]r_1[/tex] and [tex]r_2[/tex] in terms of x?
  4. Mar 16, 2008 #3
    r1 + r2 = x
  5. Mar 16, 2008 #4
    If r1 is the distance from mass 1 to mass 3, and r2 is the distance from mass 3 to mass 2, and the distance between mass 1 and mass 2 is 61.2, then what is r2 (the distance between mass 3 and mass 2)?
  6. Mar 16, 2008 #5
    r2 = 61.2 - r1

    ok, so substitute this into the ratio r1/r2 --> r1/(61.2-r1) = sqrt (m1/m2)

  7. Mar 16, 2008 #6
    Yes, and then solve for r_1.
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