The elongation of a wire on the surface of the earth is ${10}^{-4} \mathrm{m}$. The same wire of same dimensions is elongated by $6\times {10}^{-5} \mathrm{m}$ on another planet. The acceleration due to gravity on the planet will be _____ $\mathrm{m} {\mathrm{s}}^{-2}$. (Take acceleration due to gravity on the surface of earth $=10{ \mathrm{m} \mathrm{s}}^{-2}$)

Statement I : The law of gravitation holds good for any pair of bodies in the universe.

Statement II : The weight of any person becomes zero when the person is at the centre of the earth.

In the light of the above statements, choose the correct answer from the options given below.

Four spheres each of mass $m$ form a square of side $d$ (as shown in figure). A fifth sphere of mass $M$ is situated at the centre of square. The total gravitational potential energy of the system is