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Homework Help: Net gravitational force

  1. Dec 14, 2009 #1
    Confused :(

    1. The problem statement, all variables and given/known data
    A 200 kg object and a 500 kg object are separated by 0.500 m. Find the net gravitational force exerted by these objects on a 50.0 kg object placed midway between them.
  2. jcsd
  3. Dec 14, 2009 #2


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    Gold Member

    We don't spoonfeed homework here. Show your attempts.
  4. Dec 15, 2009 #3
    I have:
    F= Gm1m2/r^2
    F= G(50.0kg)(500kg-200kg)/0.25m^2 =240000N toward 500kg

    I feel that I have it setup right but for some reason when I calculate I get 2400000 which seems wrong to me.
  5. Dec 15, 2009 #4


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    What value have you used for G?
  6. Dec 15, 2009 #5

    9.8 m/s^2
  7. Dec 15, 2009 #6


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    Gold Member

    That's little g. You want http://en.wikipedia.org/wiki/Gravitational_constant" [Broken].
    Last edited by a moderator: May 4, 2017
  8. Dec 15, 2009 #7
    Any advice on how I find it?
  9. Dec 15, 2009 #8
    Your working the same problem?
  10. Dec 15, 2009 #9

    The easiest way, I would think, would be to click on the link DaveC provided under 'big G'. :smile:
  11. Dec 15, 2009 #10
    If it was a snake it would have bitten me.

    So G is 6.674 x 10^-11N (m/kg)^2 correct?

    That would mean my equation is:
    F= 6.674 x 10^-11(50.0kg)(500kg-200kg)/0.25m^2 =1.60176 x 10^-5N toward 500kg?
    Last edited: Dec 15, 2009
  12. Dec 15, 2009 #11


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    Homework Helper

    No, you don't subtract the masses.

    Calculate the forces separately, between the 200&50 kg masses, and then between the 500&50 kg masses. Then use vector addidtion to add these two forces together. Important: add the forces as vectors, don't just add the two numbers together.
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