Two identical spheres are placed in contact with each other. The force of gravitation between the spheres will be proportional to ($R =$ radius of each sphere).

Explain the principle of superposition for gravitational force.

$A$ rocket is fired from the Earth towards the Sun. At what distance from the Earth's centre is the gravitational force on the rocket zero? Mass of the Sun $= 2 \times 10^{30} \; kg$,mass of the Earth $= 6 \times 10^{24} \; kg$. Neglect the effect of other planets,etc. (Orbital radius $= 1.5 \times 10^{11} \; m$)

If the mass of a body is $M$ on the Earth's surface,then the mass of the same body on the Moon's surface is:

Two spheres of masses $m$ and $M$ are situated in air and the gravitational force between them is $F.$ The space around the masses is now filled with a liquid of specific gravity $3.$ The gravitational force will now be

Four identical particles of mass $m$ are kept at the four corners of a square. If the gravitational force exerted on one of the masses by the other masses is $\left(\frac{2 \sqrt{2}+1}{32}\right) \frac{Gm^2}{L^2}$,the length of the sides of the square is