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Homework Help: Charges problem.

  1. Jan 27, 2004 #1
    Four charges are arranged in (x,y) plane:
    -3nC at (-4, 1)
    -4nC at (0, 0)
    -6nC at (5, 3)
    -7nC at (4, 5)

    Find the magnitude of the resulting force charge at the origin(0, 0).

    I know how to find radius:
    R1(squared) = 17
    R2(squared) = 0
    R3(squared) = 34
    R4(squared) = 41

    But I don't know which charges to use in the equation to find four different forces:
    F=(K*q1*q2)/r(sqared)
    K = 8.99 * 10^9

    Can someone please help me?
     
  2. jcsd
  3. Jan 27, 2004 #2
    Find the field at the origin by other charges exluding the one which is placed at the origin(* NOTE *) Add vectorially
     
  4. Jan 27, 2004 #3
    posted the question wrong

    Find the magnitude of the resulting force on the -4nC charge at the origin.

    And radius' are suppose to be from that charge, so they are only 3 radius.
     
  5. Jan 27, 2004 #4
    Yes , but F is vector u can not add only magnitudes it has to be done in proper manner
     
  6. Jan 27, 2004 #5
    Tell me if I'm doing this right, I'm getting big numbers thta's why I have a doubt:

    F1 = 8.99e9*4e-9*3e-9/17 = 6.346e-9
    F2 = 8.99e9*4e-9*6e-9/34 = 6.346e-9
    F3 = 8.99e9*4e-9*5e-9/41 = 4.385e-9

    Ang1= tan^-1(1/-4) = -14.04
    Ang2= tan^-1(3/5) = 30.96
    Ang3= tan^-1(5/4) = 51.3

    Am I right so far?
     
  7. Jan 27, 2004 #6
    Let the forces be in form Kq1q2/r^2

    Yes angles are correct but what are the directions of these vectors??



    After finding the direction resolve the components along x&y axis And now add the components
     
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