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Homework Help: Electric Force

  1. Jan 25, 2012 #1
    1. The problem statement, all variables and given/known data

    1. Charge q1= 1.00*10^-9C is located +0.01 m from the origin along the x-axis. Charge q2= 2.00*10^-9C is located +0.03 m from the origin. What is the electric force exerted by these two charges on a third charge, q3= 1.5*10^-9C, located at the origin?

    a. 1.65*10^-4N

    *b. 1.4*10^-4N

    c. 4.4*10^-4N

    d. 6.1*10^-4N

    2. Relevant equations

    F=kq1q2/r^2
    Ftotal=F1+F2...Fn

    3. The attempt at a solution

    both charges q1 and q2 exert a repelling force in the same direction with different magnitudes on charge q3

    Ftotal=Fq1+Fq2
    Ftotal=kq1q3/r1-32+kq2q3/r2-32
    Ftotal=kq3((q1/r1-32)+(q2/r2-32))
    Ftotal=9x109*1.5x10-9(1.0x10-9/(.01)2)+(2.0x10-9/(.03)2))
    Ftotal=1.65x10^-4

    the answer key says it is supposed to be B but I get A...what am I doing wrong?
     
  2. jcsd
  3. Jan 25, 2012 #2

    gneill

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    Staff: Mentor

    Are you sure that all three charges are located along the x-axis?
     
  4. Jan 25, 2012 #3
    It doesnt specify, so I assumed since the first one is along the x axis the second one is two.
     
  5. Jan 25, 2012 #4

    gneill

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    Staff: Mentor

    Suppose, just for the sake of curiosity, that the second charge was located at y = +0.03m on the y-axis. What would the net force magnitude be on q3 at the origin?
     
  6. Jan 25, 2012 #5
    1.38x10^-4 so it was supposed to say it was at the y axis
     
  7. Jan 25, 2012 #6

    gneill

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    Staff: Mentor

    That would be my guess, yes.
     
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