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Homework Help: Calculate the magnitude and direction of the net electric force

  1. Jan 13, 2012 #1
    1. The problem statement, all variables and given/known data

    Three point charges lie along a straight line as shown in the figure below, where q1 = 6.60 µC, q2 = 1.41 µC, and q3 = -1.9 µC. The separation distances are d1 = 3.00 cm and d2 = 2.00 cm. Calculate the magnitude and direction of the net electric force on each of the charges.


    I need to state the magnitudes and directions of all 3 charges.

    2. Relevant equations


    3. The attempt at a solution

    I have to convert the values to be able to properly use the equations.
    q1=6.60e-9 C
    q2=1.41e-9 C
    q3=-1.9e-9 C
    d1=.03 m
    d2=.02 m

    I think I will only need help with the first part, I then should be able to do the rest on my own.
    between q1 and q2:
    [itex]F_{e}=(8.9876e9)\frac{|6.60e-9||1.41e-9|}{.03^{2}}=9.29e-5[/itex]to the left

    between q1 and q3:
    [itex]F_{e}=(8.9876e9)\frac{|6.60e-9||-1.9e-9|}{.05^{2}}=4.51e-5[/itex] to the right

    I will now subtract the answers: (9.29e-5)-(4.51e-5)=4.78e-5
    The force to the left is greater than the force to the right, so it will move to the left.

    When I put this answer it says "Your response differs significantly from the correct answer."
    The to the left part is obviously right.

    What did I do wrong here?
  2. jcsd
  3. Jan 13, 2012 #2

    Doc Al

    User Avatar

    Staff: Mentor

    I haven't looked at the rest of your work, but these are not quite right. Realize that μ means 10-6, not 10-9.
  4. Jan 13, 2012 #3
    Thanks a lot, I did have the conversions wrong.
    I re worked it out and came up with the correct answer of 47.8 to the left.
    Thanks again.
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