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Homework Help: Resolving the electric force into x y components?

  1. May 28, 2017 #1
    1. The problem statement, all variables and given/known data
    A 64 microC charge is locate 30 cm to the left of a 16 micro C charge. What is the resultant force
    on a -12 micro C charge positioned exactly 50 mm below the 16 micro C charge?

    2. Relevant equations

    coulomb law f=k*qq/(r^2),resultant force,resolve into x and y component.
    3. The attempt at a solution

    the first three steps are straightforward
    first step
    using Pythagoras rule gives s=58.3 mm and theta = 59.0 degree
    the force b/w q1 and q2 using coulomb law i calculated
    F13 = 2033 N.
    similarly ,the force between q2 and q3, gives correctly
    F 23= 691 N.
    i am having trouble understanding these steps about resolving it into components.i need some revision here.

    Fx = 0- F13 cos 59.0 (where does the zero come from?)
    = -(2033 N) cos 59.0
    which gives Fx = -1047 N
    Fy = F23 + F13 sin 59.00(why add force 23)
    = 691 N + (2033 N) sin 590
    Fy = 2434 N
    i can do the rest.

    Attached Files:

    Last edited: May 28, 2017
  2. jcsd
  3. May 28, 2017 #2
    also it says
    F13=2033 N ,59 degree north of West.
    F23=691 newton,Upward.

    I dont get how these directions come and what they mean in the answers.
  4. May 28, 2017 #3
    anyone help here.i am revising tons of questions and this is standing in the way or preventing me from proceeding .
    Thank you
  5. May 28, 2017 #4


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    Science Advisor
    Homework Helper
    Gold Member

    This is one of those threads where it all seems so straightforward that I might misunderstand where your difficulties lie, so bear with me.
    The 0 represents the x component of the force between q2 and q3.
    It looks like "F12" means the force exerted on q2 by 1, etc. In the y direction, you have both F23 and a component of F13.
    F13 acts along the hypotenuse of the triangle. As you calculated, that is at 59 degrees to the x axis; specifically, 59 degrees N of W.
    Unfortunately, if you make a second post to your own thread it no longer shows as "unanswered", so tends to take longer to get an answer. Better to edit your initial post.
  6. May 28, 2017 #5
    greatly appreciated.
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