# Homework Help: Electric field, force on charge

1. Feb 18, 2010

### Patrickas

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

q1 = 10^-9 C
q2 =16*10^-9 C
Distance between q1 and q2 is 7*10^-3m
What force will affect a q3=2*10^-9 charge, which is 3*10^-3m from the q1 and 4*10^-3m from q2?

2. Relevant equations

So the triangle is not right angled which means i cant use the pitagorean theorem.
ok so i think i nede to use E=q/4*pi*electric const*r^2
And when i find the e3 i would use F=E3q3

3. The attempt at a solution

So i find the E1=10^7C/C and E2=0.9*10^7N/C then i get stuck at trying to get the E3

I also tried http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html multiple point charges got the e3 but when put into F=E3*q3 i get the 3.6*10-2 where the answer is 2*10^-3

Last edited: Feb 18, 2010
2. Feb 18, 2010

### thebigstar25

I think E1 should be 10^6 N/C .. what value of E3 you used?

3. Feb 19, 2010

### Patrickas

lol it wasnt a triangle. i got it right now