The gravitational intensity at the centre $O$ of a hemispherical shell of uniform mass density has the direction indicated by which arrow?

$A$ 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

$A$ uniform sphere has radius $R$ and mass $M$. The magnitude of the gravitational field at distances $r_1$ and $r_2$ from the centre of the sphere are $E_1$ and $E_2$ respectively. The ratio $E_1: E_2$ is ($r_1 > R$ and $r_2 < R$).

The mass of the moon is $\frac{M}{81}$,where $M$ is the mass of the earth. The distance between the earth and the moon is $60R$,where $R$ is the radius of the earth. At what distance from the center of the moon will the gravitational intensity be zero (in $R$)?

At what distance from the centre of the moon is the point at which the strength of the resultant gravitational field of the Earth and the Moon is equal to zero (in $,R$)? The Earth's mass is $81$ times that of the Moon,and the distance between the centres of these bodies is $60\,R$,where $R$ is the radius of the Earth.

Gauss's law for gravitation is given by: