1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Three Point Charges, Find x-component

Tags:
  1. Jan 16, 2015 #1

    rlc

    User Avatar

    1. The problem statement, all variables and given/known data
    In the figure, three point charges are arranged in a equilateral triangle of side a= 1.40×10-2 m. Sketch the field lines due to + Q and -Q, where Q = 2.50×10-5 C , and from them determine the direction of the force that acts on +q = 5.00×10-8 C because of the presence of the other two charges. What is the x-component of the force? What is the y-component of the force?
    upload_2015-1-16_13-18-25.png

    2. Relevant equations
    F1=K*((Q*q)/a^2)
    F(x)=2|F1|*Cos(60)

    3. The attempt at a solution
    I know that the y-component is 0 N.
    Someone posted this problem in yahoo answers, and I tried to follow it. Something went wrong along the way, but here is the work from that solution:

    *+Q=1, -Q=2, +q=3*

    F1,3=(8.99E9)(5.00E-8)(2.50E-5)/(1.40E-2)=0.803 N
    F2,3=(8.99E9)(5.00E-8)(-2.50E-5)/(1.40E-2)=-0.803 N

    F1,3x=0.803(cos(30 degrees))=0.6951 (right)
    F1,3y=0.803(cos(60))=0.4013 (down)

    F2,3x=-0.803(cos(30))=-0.6951 (left)
    F2,3Y=-0.803(cos(60))=-0.4013 (down

    Here, I have the problem where if you combine x and y values, the answer is 0 for both of them.
    Where did I go wrong, or is all of this wrong?
     
  2. jcsd
  3. Jan 16, 2015 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Get rid of that negative sign. Use Coulomb's law to find the magnitude of the force, then use the signs to find the direction. Draw yourself a diagram of the forces on q.
     
  4. Jan 20, 2015 #3

    rlc

    User Avatar

    Sorry for not replying in a while!
    In the work I did, I completely forgot to square a, making all my numbers wrong.

    ((9E9)(q)(+Q))/(a^2)
    ((9E9)(5.00E-8)(2.50E-5))/(1.40E-2)^2=57.33 N (this is the x-component)

    Thank you!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted