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Homework Help: Having hard time understanding Universal gravity Law

  1. Jul 18, 2008 #1
    1. The problem statement, all variables and given/known data

    A long line connecting Earth and the Moon, at what distance from Earth's centre would an object have to be located so that the gravitational attractive force of Earth on the object was equal in magnitude and opposite in direction from the gravitational attractive force of the Moon on the object?

    I honesty have no idea how to do this. I've read the text book but i still cant solve the problem, which probably means I dont fully understand the gravity law :-(
  2. jcsd
  3. Jul 18, 2008 #2


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    Do you happen to know the distance between the Earth and the Moon?
  4. Jul 18, 2008 #3


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    Aside from the absurdity of a line between the two, and the rotational forces etc. I think what they are asking you to consider is that if you put an object between a mass the size of earth and a mass the size of the moon - both separated at their current distance - at what point would the gravitational attraction between the earth and the object also equal the gravitational attraction of the moon and the object.

    Do you have the formula for gravitational attraction between 2 bodies?
    Last edited: Jul 18, 2008
  5. Jul 18, 2008 #4
    is it Fg = G(m1m2/r^2)?
    and no I wasnt given the distance between earth and moon.
  6. Jul 18, 2008 #5

    Doc Al

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    The distance between them, as well as their masses, can be readily looked up.
  7. Jul 18, 2008 #6


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    Yes … but you'll need an m3 also, won't you?

    And an r1 and r2. :smile:
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