Two identical conducting spheres P and S with charge Q on each, repel each other with a force 16 N. A third identical uncharged conducting sphere R…

Two identical conducting spheres $\displaystyle P$ and $\displaystyle S$ with charge $\displaystyle Q$ on each, repel each other with a force $\displaystyle 16$ N . A third identical uncharged conducting sphere $\displaystyle R$ is successively brought in contact with the two spheres. The new force of repulsion between $\displaystyle P$ and $\displaystyle S$ is :