In: Physics
The point where we want to evaluate electric potential is at distance away from charge q1, and away from q2. The electric potential at this point is the sum of electric potential due to charges q1 and q2.
The potential energy of two charges q1 and q2 separated by a distance r is
The two charges are separated by r=25cm=0.25m
When the two charges are separated by distance r=5cm=0.05m, the potential energy is
Work done by the system is equal to the change in potential energy of the system
Note that the work done by the system is positive which is compatible with the result that potential energy of the system decreases (the system when r=5cm have lesser potential to do work than system when r=25cm).