Force between 2 parallel, charged, conducting sheets.

[khfrekek1992]

Homework Statement

Two square parallel sheets with area>>distance between them have total charges of Q1 and Q2 on them. What is the force between them?

Homework Equations

Q1in+Q2in=0
Q1in+Q1out=Q1
Q2in+Q2out=Q2
Q1out=Q2out

The Attempt at a Solution

I set up 4 equations for the charges on the inner and outer sides of each plate (shown above)

Now I have no idea how to find the electric field from here. any help?

 

[khfrekek1992]

Or am I doing this wrong?

 

[khfrekek1992]

This seems like such an easy problem but I have no idea where to start..