The range of gravitational forces is

The ratio of the radii of a planet and the earth is $1: 2$, the ratio of their mean densities is $4: 1$. If the acceleration due to gravity on the surface of the earth is $9.8 \mathrm{~ms}^{-2}$, then the acceleration due to gravity on the surface of the planet is

Two stars of masses $M$ and $2 M$ that are at a distance $d$ apart, are revolving one around another. The angular velocity of the system of two stars is ( $G$-Universal gravitational constant)

The ratio of the accelerations due to gravity at heights 1280 km and 3200 km above the surface of the earth is (Radius of the earth $=6400 \mathrm{~km}$ )

Regarding fundamental forces in nature, the correct statement is

The energy required to take a body from the surface of the earth to a height equal to the radius of the earth is $W$. The energy required to take this body from the surface of the earth to a height equal to twice the radius of the earth is

A ring has a mass $M$ and radius $R$. The distance of the point on its geometric axis from its centre at which the gravitational field is strongest is