Final answer:
The potential energy of two particles with like charges is positive due to the work required to bring them closer against their repulsive force. For two opposite charges, the potential energy is negative because the system does work when they attract each other.
Step-by-step explanation:
When two particles with like charges are close enough to interact, their potential energy is positive. The potential energy is positive because work needs to be done against the repulsive force to bring two like charges (either both positive or both negative) closer together. This increases the electrical potential energy of the system. In contrast, when two opposite charges are brought closer, they attract each other, and work is done by the system, which results in a decrease in potential energy, and hence the potential energy is negative.
If we take a positively charged particle exerting an inward force on another particle P, the charge of particle P will be negative because like charges repel and opposite charges attract (as per Coulomb's law).
The force between two positive point charges is repulsive and acts along the line joining the two point charges. This is a result of the electrostatic force described by Coulomb's law, which states that like charges repel each other.