$A$ hollow spherical shell is compressed to half its radius. The gravitational potential at the centre

Two heavy spheres each of mass $100 \; kg$ and radius $0.10 \; m$ are placed $1.0 \; m$ apart on a horizontal table. What is the gravitational force and potential at the mid-point of the line joining the centres of the spheres? Is an object placed at that point in equilibrium? If so,is the equilibrium stable or unstable?

$A$ stationary body on the surface of the Earth has negative potential energy. What does this indicate?

$A$ particle is kept on the surface of a uniform sphere of mass $1000 \ kg$ and radius $1 \ m$. The work done per unit mass against the gravitational force between them is $\left[G=6.67 \times 10^{-11} \ N \ m^2 \ kg^{-2}\right]$

Match Column-$I$ with Column-$II$.

Column-$I$	Column-$II$
$(1)$ Can never be positive.	$(a)$ Escape velocity
$(2)$ Reason for negative potential energy of galaxies.	$(b)$ Gravitational potential energy
	$(c)$ The nature of force between different galaxies is attractive.

An infinite number of bodies,each of mass $2 \, kg$,are situated on the $x-$axis at distances $1 \, m, 2 \, m, 4 \, m, 8 \, m, \dots$ respectively,from the origin. The resulting gravitational potential due to this system at the origin will be: