If the gravitational field intensity at a point is given by $E = K/x^3$,what is the gravitational potential at that point?

$A$ point particle is held on the axis of a ring of mass $m$ and radius $r$ at a distance $r$ from its centre $C$. When released,it reaches $C$ under the gravitational attraction of the ring. Its speed at $C$ will be

Two concentric shells have masses $M$ and $m$ and their radii are $R$ and $r$ respectively,where $R > r$. If $x$ is the distance from the common centre,what is the gravitational potential at a point for which $r < x < R$?

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

$A$ particle of mass $10\, g$ is kept on the surface of a uniform sphere of mass $100\, kg$ and radius $10\, cm$. Find the work to be done against the gravitational force between them to take the particle far away from the sphere (you may take $G = 6.67 \times 10^{-11}\, Nm^2 / kg^2$).

Three masses $200 \ kg$, $300 \ kg$, and $400 \ kg$ are placed at the vertices of an equilateral triangle with sides $20 \ m$. They are rearranged on the vertices of a bigger triangle of side $25 \ m$ with the same center. The work done in this process is . . . . . . $J$.