It is about Electric Force. Coulomb's Law.

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

Charges of -1 micro coulomb and -4 microcoulomb are placed at opposite ends of a meter ruler. Where on the ruler could...

(a) a free electron be placed and be in electrostatic equilibrium?

(b) a free proton be placed and be in electrostatic equilibrium?

**2. Relevant equations**

F=K(q1q2)/r2

F= Force (Newtons)

Q= Coulombs charges

R= distance between the charges

K= botlzmann constant

**3. The attempt at a solution**

I tried getting the answer by doing math without involving phyisics, like this:

If 4 microcolombs is 100%

then 1 microcoulomb might be 25%

and I have a 1 meter long ruler,

then the new coulomb would be placed 25% to the right from the force that has 1 microcoulomb. That would be 25 cms to the right from the -1 microcoulomb

I reach this conclusion by math logic, but I believe it's wrong and my teacher told me it really is wrong, my method is ambiguous so..

I hope someone helps me get me the correct answer.