Potential difference, electric potential energy and work

r_swayze

Four charges are arranged at the corners of a rectangle as shown in the diagram. How much work needs to be done to move the charge q2 to infinity?

Since change in PE_e = W, am I suppose to find total potential electric energy of the four charges and then subtract the total potential electric energy of the three charges without q2? Would the difference in the two potential electric energies be the work it takes to move q2 to infinity?

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willem2

That would work, but it's easier to calculate the potential from the 3 non-moving charges at the position where q2 is.