Two spheres of mass $m$ 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

The atmosphere is held to the earth by

The distance of the planet Pluto from the Sun is $40$ times the distance of the Earth from the Sun. Assuming the masses of the Earth and Pluto are equal,find the ratio of the gravitational force exerted by the Sun on the Earth to that on Pluto.

The tidal waves in the sea are primarily due to

$A$ large number of identical point masses $m$ are placed along the $x$-axis at $x = 0, 1, 2, 4, 8, \dots$ units. The magnitude of the total gravitational force on the mass at the origin $(x = 0)$ will be:

Draw a schematic diagram of Cavendish's experiment for the determination of the universal gravitational constant $G$ and obtain the formula used in it.