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Homework Help: About Gravitational Force

  1. Dec 14, 2014 #1
    1. The problem statement, all variables and given/known data
    Please look at the picture.

    2. Relevant equations
    $$F=\frac{GMm}{d^2}$$

    3. The attempt at a solution
    I'm stuck with this problem , because I cannot imagine it properly.
    If I say that the mass m is in between the two masses , I cannot find d in the choices ,, Any help please!! q23.jpg
     
  2. jcsd
  3. Dec 14, 2014 #2

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    The prompt gives you that the two large masses are separated by D, and that the small mass is somewhere between them, meaning that you are being asked for "d" in terms of "D."
     
  4. Dec 14, 2014 #3
    The mass in between would have a net gravitational force equal to :
    $$\frac{GMm}{d^2}-\frac{G(4M)m}{(D-d)^2}$$
    and that should be ZERO.
    Then solving for d won't lead to one of the choices!!
     
  5. Dec 14, 2014 #4

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    What equation are you solving?
     
  6. Dec 14, 2014 #5
    The equation is of the net gravitational force acting on smaller mass which should be zero.
     
  7. Dec 14, 2014 #6

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    WRITE the equation.
     
  8. Dec 14, 2014 #7
    $$\frac{GMm}{d^2}-\frac{G(4M)m}{(D-d)^2}=0$$
     
  9. Dec 14, 2014 #8

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    Can you eliminate GMm? Yes. Do so.
     
  10. Dec 14, 2014 #9
    Oh,,, I got it ...
    Thanks
     
  11. Dec 14, 2014 #10

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    Take things one step at a time, and they'll usually fall into place for you.
     
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