A point charge +Q is placed at the centroid of an equilateral triangle. When a second charge +Q is placed at a vertex of the triangle, the magnitude of the electrostatic force on the central charge is 4N. What is the magnitude of the net force on the central charge when a third charge +Q is placed at another vertex of the triangle?

Explanation

When the first charge +Q is placed at a vertex, it exerts a force of 4 N on the central charge due to the Coulomb's law. When the second charge +Q is added at another vertex, the forces exerted by these two charges on the central charge are equal in magnitude and symmetrically positioned. The geometry of the equilateral triangle ensures that these forces do not cancel but add up vectorially to result in a net force of 4 N, directed towards the line joining the central charge and the midpoint of the line segment between the two vertex charges. This is due to the symmetry of the triangle which maintains the same magnitude of net force as when only one charge was at the vertex.