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 8N. The magnitude of the net force on the force on the central charge when a third charge +Q is placed at another vertex of the triangle is

The magnitude of forces from both the vertex charges will be same since both charges are at equal distance from the centroid and are of same magnitude. Let the force be, whose magnitude is 8N.

When both the charges exert force on centroid charge, the angles made by the forces with each other is.

Hence the net force acting on the central charge is=F=8N