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Resultant gravitational force

  1. May 11, 2008 #1
    Hi everyone,

    Could someone please help me with this problem?
    The problem statement, all variables and given/known data
    Three uniform spheres of mass m1=2.00kg, 4.00kg, and m2=5.50 kg are placed at the corners of a right triangle. Calculate the resultant gravitational force on the 4.00 kg object, assuming the spheres are isolated from the rest of the Universe.

    2. Relevant equations
    Fg=m1m2/r^2


    3. The attempt at a solution

    F32=-6.67X10^-11Nm^2/kg(5.5kg)(4kg)/4^2= -9.2 X 10^-11i

    F13= -6.67X10^-11Nm^2/kg^2(4)(2)/3^2= 5.9X10^-11j

    Thank you very much
     
  2. jcsd
  3. May 11, 2008 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Please describe--even better, provide a diagram of--the triangle and its dimensions and the relative locations of the masses.

    Recall that forces are vectors. You find the resultant by adding up the individual force vectors (add them like vectors, not plain numbers).
     
  4. May 11, 2008 #3
    Thank you

    The triangle is placed in the second quadrent, where m3 is at (0,0) m2 is at (-4,0)m and m1 is at (0,3)

    Does this look correct?
    F32=-6.67X10^-11Nm^2/kg(5.5kg)(4kg)/4^2= -9.2 X 10^-11i

    F13= -6.67X10^-11Nm^2/kg^2(4)(2)/3^2= 5.9X10^-11j

    Thank you
     
  5. May 11, 2008 #4

    Doc Al

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    Staff: Mentor

    I didn't check your arithmetic, but your setup looks good. Now find the magnitude of the resultant force.
     
  6. May 11, 2008 #5
    Thank you

    I just need it in terms of i and j. So, wouldn't that be correct the way it is? F32 is negative and F13 is positive, right?

    Thank you
     
  7. May 11, 2008 #6

    Doc Al

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    Staff: Mentor

    The signs of your final answers are correct. But I don't know what you mean by F32 (versus F23). Is that the force on 3 from 2? Realize that you want the force on mass 3, and that F32 = -F23. (Just be consistent.)
     
  8. May 11, 2008 #7
    Thank you very much

    Regards
     
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