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Homework Help: Help With Forces of gravitational attraction

  1. Oct 7, 2004 #1
    K the question is basically where you are given the Earth's Mass (5.98*10^24kg) the moon's mass in this equation is 1.2% of the mass of the earth. (7.176*10^22kg) We are also given that the distance from the centres is 3.84*10^5km (converted to metres is 3.84*10^8)
    So I have no problems with these. (This is a bonus question by the way)
    The question states that somewhere along this line, the force of gravity is zero. But when i try to solve the eq'n i keep getting undefined answers.

    So can anyone point me in the right direction?

    K since this seems to not make much sense i'll rephrase it.

    There is a point between the Earth and the Moon where the Force of Gravity is ZERO Newtons, By knowing the mass of the two masses, the distance between the masses and the Gravitational Constant, how can i find where Fg = 0
    Last edited: Oct 7, 2004
  2. jcsd
  3. Oct 7, 2004 #2


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    I'm having a little trouble verifying your equation, as I'm not sure what's a subscript and what's a quantity. You might want to check that. However, I suspect your problem is more mathematical than physical.

    Remember - the r's in your equation will be measured from two different points. Just for the sake of argument, let's say that r1 is the distance from the Earth's center and r2 is the distance from the moon's. At the point of gravitational equlibrium, these will not be the same. However, if R is the distance between the centers, then you could express them as r1 and (R - r1), removing one variable. Since you know R, the rest should be easy.

    Hope this helps.
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