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Homework Help: Potential Energy of a Three-Particle System

  1. Nov 21, 2004 #1
    I am working on this problem:

    Four uniform spheres, with masses mA = 200 kg, mB = 100 kg, mC = 1900 kg, and mD = 250 kg, have (x, y) coordinates of (0, 50 cm), (0, 0), (-80 cm, 0), and (40 cm, 0), respectively. Sphere A is then removed. Calculate the gravitational potential energy of the remaining three-particle system

    And I do not understand why I cannot get the correct answer. Potential energy equals...

    = -G(m1m2)/r

    Or in my case...
    = -G(100*1900/80 + 100*250/40 + 1900*250/120)
    = -4.6433E-7 J

    Do I need to account for the loss of sphere A? Or is my error not accounting for the opposite direction of sphere C? Thanks for any advice.
  2. jcsd
  3. Nov 21, 2004 #2


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    Hm..did you convert cm's into m's?
  4. Nov 21, 2004 #3
    Wow, I can't believe I'm that dumb. Thanks! :)
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