What is the acceleration due to gravity at the centre of the earth (in $m/s^2$)?

State whether the following statement is True or False:
The acceleration due to gravity $g$ is given by the formula $g = GM/R^2$,where symbols have their usual meanings.

$A$ ball is thrown vertically upwards with a velocity $u$. Calculate the velocity with which it falls to the earth again.

The atmosphere is held to the earth by

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

$A$ man throws a ball of mass $0.5 \, kg$ vertically upward with a velocity of $25 \, m s^{-1}$. Find: $(a)$ the initial momentum of the ball,$(b)$ the momentum of the ball at the halfway mark of the maximum height. (Given $g = 10 \, m s^{-2}$)