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!

Electric Forces

  1. Sep 13, 2013 #1


    User Avatar

    1. The problem statement, all variables and given/known data

    Two point charges are 3 m apart and their combined charge is 20µC. If they
    repel each other with a fore of 0.075 N, what are the two charges? Ans: 15 μC and 5μC  

    2. Relevant equations


    (could someone mention in their response how we use the math text in our posts, so that I can make it more convenient for the reader)

    3. The attempt at a solution

    I'm really not so sure where to begin here, but I made a few attempts by manipulating both q2 and q2. I will post one of them below:

    9*109 (q1+q2)/32=0.075N
  2. jcsd
  3. Sep 13, 2013 #2

    Doc Al

    User Avatar

    Staff: Mentor


    Check out the FAQ, under "SITE INFO/Frequently Asked Questions" at the top of every page.

    The one mistake you made was to use q1+q2 instead of q1*q2.

    The second equation you'll need is q1+q2 = ??
  4. Sep 13, 2013 #3


    User Avatar

    I tried that in one of my attempts, but I don't see the "bridge" between the two equations.

    If I solve Coulombs equation for q1*q2, I don't see where I'm supposed to plug in q1+q2 = 20 into the other equation....?
  5. Sep 13, 2013 #4

    Doc Al

    User Avatar

    Staff: Mentor

    You'll have two equations and two unknowns. Solve them simultaneously, using any method you like. (Such as substitution.)
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Electric Forces
  1. Electric Force (Replies: 3)

  2. Electric Force (Replies: 5)

  3. Electric force (Replies: 5)

  4. Electric Force (Replies: 13)