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Physics is generally pretty hard for me, so understanding Electric forces has been a monster. I've done what I "know" how to do on the following problem, but I need some input from the professionals =) Thank you in advance.

Two point charges, Q1 and Q2 are located a distance .20 meter apart. Charge Q1= +8.0 (Mu)C. The next electric field is zero at point P, located .40 meter from Q1 and .20 meter from Q2.

1. Determine the magnitude and sign of charge Q2.

I don't know how to get the answer, but I realize the magnitude is the force acting on Q2. So, F=k(q1 x q2)/(r^2). The total force acting on Q2 would have to include both P and Q2, so F=k(Q1Q2)/(.2^2)+k(Q2P)/(.2^2).

Since the E field around P is 0..

E=k x (P)/(r^2)

0=k x q/(.2^2) + k x q/(.4)^2

I'm clueless on getting the actual force, I only know Q1 and I don't know P. What can I do here?

2. Determine the magnitude and direction of the net force on charge Q1. No idea.

3. Calculate the electrostatic potential energy of the system.

qV=UE V=k x (q/r)

q1 x k x (q1/r) + q2 x k x (q2/r) + P x k x (P/r)

The rest on this part is dependent on above.

4. Determine the coordinate of the point R on the x-axis between the two charges at which the electric potential is zero.

Again, I don't know what to do.

5. How much work is needed to bring an electron from infinity to point R, which was determined in the previous part?

Dependent on above.

Even though this looks like the work of a slouch, it's really my best effort. I, again, thank you for any assistance you provide.