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: Point Charges simple Question

  1. Apr 21, 2008 #1
    1. The problem statement, all variables and given/known data
    Charge A and charge B are 3.00 m apart, and charge A is +2.00 C and charge B is +3.00 C. Charge C is located between them at a certain point and the force on charge C is zero. How far from charge A is charge C?

    2. Relevant equations

    3. The attempt at a solution
    I am reviewing for my final and I can't remember how to do this!!! I wanted to use...
    F = K*Q1*Q2 / r^2
    But I can't have 0 in the denominator so I know I am missing something obvious...but I am not seeing it.
  2. jcsd
  3. Apr 21, 2008 #2
    you're solving for when the NET force is zero. let A be charge of A, B be charge of B, and C for C, etc. distance d apart. so the distance from C to A is R1, and C to B is R2 then R1 + R2 = d.
    and the 2 forces need to equal eachother - i.e. F1 = kAC/(R1^2) = kBC/(R2^2) does that make sense?
  4. Apr 21, 2008 #3
    Well yea but I don't have R2? So I tried using like R2 = 3- R1 but I can't get that to work...
  5. Apr 21, 2008 #4
    thats how you have to do it, R1 and R2 are linked by the constant d (3 in this case). you'll end up with a binomial or something that you can solve numerically if nothing else.
    A/(R1^2) = B/(3-R1)^2
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook