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Gravitational force for a ball and particle

  1. Mar 10, 2014 #1
    1. The problem statement, all variables and given/known data
    How far from a very small 110kg ball would a particle have to be placed so that the ball pulled on the particle just as hard as the earth does?


    2. Relevant equations

    Fg= gMm/r^2

    3. The attempt at a solution
    I used the equation and plugged in the numbers for the ball and the earth, but then I realized that I needed to use the mass for the particle. However, I don't know what the mass for the particle is.
     
  2. jcsd
  3. Mar 10, 2014 #2

    PhysicoRaj

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    Gold Member

    It does not require the mass of the particle.
     
  4. Mar 10, 2014 #3
    Am I supposed to leave it as a variable?
     
  5. Mar 10, 2014 #4

    PhysicoRaj

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    Gold Member

    It's your choice..if you do that, you can see it cancels out ultimately.
     
  6. Mar 10, 2014 #5
    Thanks! I see it now... I end up getting R= R^2 * Mball/Mearth I'm hoping I'm in the right direction.
     
  7. Mar 10, 2014 #6

    PhysicoRaj

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  8. Mar 10, 2014 #7
    I get 7.49-10^-10 but it says I'm wrong.
     
  9. Mar 10, 2014 #8
    Whoops. I'm sorry. I forgot to square root that. Thanks so much for your help! Now to tackle the other 2 monstrous problems.
     
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