Question

Three charges are located at the corners of a rectangle as follows:
Charge A: lower left corner, -3.0 μC
Charge B: upper left corner, -6.1 μC
Charge C: upper right corner, +2.7 μC
The distance between A and B is 0.16 m and between B and C it is 0.25 m.
How much work must an external force acting on the particles (like, your hands) do in order to move the charges infinitely far from each other?

Answer 1

Simple.

The energy to do this will be equal to the PE the system has:
PE=k(Q1*Q2)/d12 +k(Q1Q3)/d13 +kQ2Q3/d23

And what is neat, you do this by moving only two charges, that puts all three infinitely apart.

Answer 2

1.49J