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Homework Help: Vector Addition of Electric Forces in a Plane

  1. Jan 21, 2008 #1
    The problem I'm trying to solve involves the effect that two charges has on a third and I need to find the magnitude of the resulting force. In this particular problem it's the effect of A and B on C.

    The work I've done so far is attached so please take a look. I've been trying to add together the x and y components of each force to find the total, but any answer I've come up with is not accepted. Any help is appreciated.

    Attached Files:

  2. jcsd
  3. Jan 21, 2008 #2


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    Homework Helper

    didn't you misplaced your results in the end, lad?

    you have 1 force with 2 components (as your established axis implies) and another force 1 component.

    I see you've written Fx = (number) + 0 which doesn't make sense with your previous work.

    The result will be obtained by

    [tex] \vec{R} = \vec{F}_{AC} + \vec{F}_{BC} [/tex]
  4. Jan 21, 2008 #3
    Ok so I've been trying to that exact thing. Since there is a repulsion between A and C, F_AC will be negative yes? And F_BC will be positive due to the attraction between B and C? Something has to be wrong with those assumptions on my part since I've checked the math repeatedly and F_AC + F_BC is not giving me a correct answer.
  5. Jan 21, 2008 #4


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    I checked your numbers, the result is other, you might have made a mistake in the component addition to obtain the resultant magnitude or in calculating the resultant magnitude. Everything else is fine.
  6. Jan 24, 2008 #5
    So the magnitude of the total force equals F_ac + F_bc. If this is true, then masteringphysics should be accepting my answer of 2.83*10^-5, which it is not. I'm very frustrated at this point. I've only entered 8 possible answers with nothing correct. I know there has to be some silly little mistake I'm making here.

    It accepted my answers for the first two parts of the question. The sum of the x components is 8.47*10^-5 and the sum of the y components is -5.64*10^-5. Like you said, my math is correct, at least in respect to that portion of the question.
    Last edited: Jan 24, 2008
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