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: Easy homework problem I know, how original.

  1. Sep 7, 2007 #1
    1. The problem statement, all variables and given/known data
    Four point charges are situated at the corners of a square with sides of length a.
    Find the resultant force on the positive charge q. HINT: write an expression for the resultant force, use Ke for Ke, q for q, and a for a! That makes sense, because not much information is given.

    HERE is a picture.

    2. Relevant equations

    F=Ke ( q1q2 / m^2 )

    Ke is the constant 8.99e9 Nm^2/C^2.

    Q1 and Q2 are any two charges of interest. That m^2 basically means the distance between two should be charges squared. So if distance between two charges is 5 cm, then it should be (0.05m)^2.

    3. The attempt at a solution

    F of top left negative charge on positive charge = Ke ( q^2 / a^2 ) ?

    F of top right negative charge on positive charge =Ke ( q^2 / ( (2sqrt(a))^2 ) ?

    F of bottom right negative charge on positive charge = Ke ( q^2 / a^2 ) ?

    I don't know what I'm doing.
    I figured that if you make a 45 45 90 triangle out of that square, the length between the positive charge and the top right charge should be 2sqrt(a). Other than that I do not know.
  2. jcsd
  3. Sep 7, 2007 #2


    User Avatar
    Homework Helper

    That distance should be [tex]\sqrt{a^2+a^2} = a\sqrt{2}[/tex] So the distance square is just 2a^2.

    Draw a picture of the 3 force vectors... You need to add the 3 vectors... but the problem can be simplified when you see the symmetry...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook