What will be the mass of a body at the centre of the earth as compared to other places on the earth?

$A$ stone is dropped from the edge of a roof. It passes a window $2 \, m$ high in $0.1 \, s$. How far is the roof above the top of the window?

Do the gravitational forces obey Newton's third law of motion?

State the source of centripetal force that our earth requires to revolve around the sun. List the factors on which this force depends.

Suppose a planet exists whose mass and radius both are half that of Earth. Calculate the acceleration due to gravity on the surface of this planet.

The value of $g$ on the earth's surface is $9.8 \, m s^{-2}$. Suppose the earth suddenly shrinks to one-third of its present size without losing any mass. What is the value of $g$ on the surface of the shrunk earth (in $, m s^{-2}$)?