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