Final answer:
The force between a +3q and a -q charge that have been in contact and returned to their original positions will be attractive based on Coulomb's law. The net force on a -q charge equidistant from a +2q and -2q dipole will also be attractive towards the positive charge of the dipole.
Step-by-step explanation:
The question involves understanding the principles of Coulomb's law, which describes the electric force between two charges. When a +3q and a -q charge come into contact and then return to their original positions, the force between them will be attractive, as they have opposite charges. This can be observed in diagrams such as Figure 18.16(b), showcasing that opposite charges exert an attractive force on each other.
Given an electric dipole with charges +2q and -2q, and a third charge -q placed equidistant from the dipole charges, the net force on the third charge will be directed towards the positive charge of the dipole, resulting in an attractive force. This is due to Coulomb's law stating that unlike charges attract, as depicted in Figure 18.26(b).