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!

Homework Help: Trouble with electric force question

  1. Dec 20, 2013 #1
    1. The problem statement, all variables and given/known data
    I'm having a little trouble with an electric force question I have been working on. It seems simple, but my answer keeps coming out incorrect. Using the graph, deduce the electric force vector on charge q3 by q1/2. In case it is not clear, q3 lies on point (2,2)

    2. Relevant equations


    3. The attempt at a solution
    Okay, well since electric force vectors simply add to give resultant force I can deduced the individual vectors and sum, as such.


    and the same applies to the second charge


    then I deduced r for both. Simply being 2 for q(2/3), and 5 for q(1/3) (from pythagoras)
    Then, the unit vectors, as (2[itex]\hat{i}[/itex]+[itex]\hat{j}[/itex])/5 for q(1/3)
    and [itex]\hat{j}[/itex] for q(2/3)

    Put it together I got


    Evaluate and sum, I got, 0.367[itex]\hat{i}[/itex]-0.412[itex]\hat{j}[/itex]

    which of course is not correct. I'm sure there is a mistake in there but can not find it. Would be greatful for some fresh eyes to tell me where.

    Thank you in advance. :)
  2. jcsd
  3. Dec 20, 2013 #2


    User Avatar
    Homework Helper
    Gold Member
    2017 Award

    Hello con31772 and welcome to PF!

    Oops. Check what you got for r for q(1/3).
  4. Dec 20, 2013 #3
    Oops. Check what you got for r for q(1/3)

    Haha, thanks very much. Could not find my mistake at all.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted