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Homework Help: Gravitational Force of Three Identical Masses Problem

  1. Jun 29, 2014 #1
    1. The problem statement, all variables and given/known data
    Three identical very dense masses of 8000kg each are placed on the x axis. One mass is at x1 = -140cm , one is at the origin, and one is at x2 = 440cm . What is the magnitude of the net gravitational force Fgrav on the mass at the origin due to the other two masses?
    Take the gravitational constant to be G = 6.67Ɨ10āˆ’11Nā‹…m2/kg2 .

    2. Relevant equations

    3. The attempt at a solution
    I have tried everything, but Mastering Physics still gives me this message: Although the two masses not at the origin are identical, they are not the same distance from the origin, so there will be a nonzero net force on the mass at the origin. Am I adding the vectors wrong? I got 2.1*10^-3
  2. jcsd
  3. Jun 30, 2014 #2


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    i think it would be better if you show how you get this number. But I think you are on the right direction when you mention vector addition and the right formula you refer to.
  4. Jun 30, 2014 #3


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    Force has dimension. As long as your answer is dimensionless it is going to be wrong.

    Assuming the intended unit is Newton, it seems to be in the right ballpark. Did you round your results during computation? It would be much easier to judge if you had posted your work.
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