Net electrostatic force on charge between parallel plates

[jh12]

I am having some trouble getting started with this problem. Do I want to use kq/r^2 at all or should I be doing something else?

The problem is:

Two point charges, Q1=-6.7 microCoulombs and Q2= 1.3 microcoulombs, are located between two oppositely charged plates. (The positively charged plate is located nearer to Q1 and the negatively charged plate is located closer to Q2). The two point charges are separated by a distance of x= 0.34m. Assume that the electric field produced by the charged plates is uniform and equal to E=73,000N/C. Calculate the net electricstatic force on Q1 and give its direcion.

 

[Doc Al]

Do I want to use kq/r^2 at all or should I be doing something else?

You need find the net force on Q1. To find the force on Q1 due to Q2, you'll need Coulomb's law, which is almost that formula. But you also need the force on Q1 due to the uniform field from the plates.

 

[jh12]

I know i need to do k(q1)(q2)/(r^2) for that force but I am confused as to how to calculate the force for the electric fields. I know F=qE but I am unsure if each plate would exert an equal E value...

 

[Doc Al]

I know F=qE but I am unsure if each plate would exert an equal E value...

I think you're given the total E field from both plates. (You still have to figure out its direction.)

 

[jh12]

so q(E) in the left direction would be the force from both plates then?
so the total force on q1 would be
q1(E) - (k)(q1)(q2)/(r^s) ?

 

[Doc Al]

Since you didn't provide a diagram, I don't know the orientation of q1 and q2 or the plates--so I don't know if the force is to the right or to the left. (But it will be something like that.)