Electrostatic, Electric Field,Electrostatic potential energy

[blee22]

Homework Statement

In the figure below, a right triangle, determine the magnitudes of the
a. Net e-field at p (assume a proton is placed at p)
b. Net electrostatic force at P
c. Net electrostatic potential at P
let q = 1.70 x 10^-8, R = 78cm and P is halfway between Q1 and Q3
Red dot is P

A^2 + B^2 = C^2 C = Sqrt(78^2+78^2)= 78sqrt(2)

Homework Equations

F= (K|q1q2|)/R^2
E= (k|q|)/ R^2
PE = (kq1q2)/R

The Attempt at a Solution

I just had a question about this problem, Since a proton is at the center, would Q1 and Q3 just cancel out since there are repelling one another and are the same charge?

If that is true would i just solve everything for the two point charges, proton and Q2 since i know what R would be between the two?

 

[RedDelicious]

When you're not sure if you can trust your intuition or the apparent symmetry, you can always fall back on the math for reassurance.

The principle of superposition tells us that when you have a system of charges, the electric field at a point is the vector sum of all of the individual fields produced by the charges at that point. So when you sum the individual electric field contributions at point P, do E1 and E3 actually sum to zero?