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Homework Help: Is my book wrong or am I?

  1. Apr 17, 2008 #1
    1. The problem statement, all variables and given/known data
    Find the total gravitational potential energy of the three masses.


    2. Relevant equations
    U=-GMm/r


    3. The attempt at a solution

    U between the 10 kg mass & the 20kg mass
    -(6.67*10^-11)(20kg)(10kg)/.20 m = -6.67 * 10 ^-8 J

    U between the 20kg mass and the 5 kg mass
    -(6.67*10^-11)(20kg)(5kg)/.10m = -6.67*10^-8 J

    U between the 10 kg mass & the 5 kg mass
    -(6.67*10^-11)(10kg)(5kg)/.2236 m = -1.49 * 10^-8 J

    adding them up I got -1.483*10^-7 J

    but the back of my book says -1.96 * 10^-7 J

    Am I doing something wrong?
     

    Attached Files:

  2. jcsd
  3. Apr 18, 2008 #2

    alphysicist

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    Homework Helper

    Hi bcjochim07,

    The image file is not ready to view. Is it simple enough to describe in words?
     
  4. Apr 18, 2008 #3
    A 10 kg mass is located 20 cm directly above a 20 kg mass. And 10 cm to the right of the 20kg mass is a 5kg mass. The masses form a right angle
     
  5. Apr 18, 2008 #4

    alphysicist

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    Your answer looks right to me.
     
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