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

$A$ ball is dropped from a height of $20\, m$. $A$ second ball is thrown downwards from the same height after one second with initial velocity $u$. If both the balls reach the ground at the same time, calculate the initial velocity of the second ball. (Take $g = 10\, m s^{-2}$).

Will a body weigh more on the equator or at the poles?

The Earth is acted upon by the gravitation of the Sun,even though it does not fall into the Sun. Why?

$(i)$ How is the force of attraction dependent on the masses of objects and the distance between them?
$(ii)$ The mass of the Earth is $6 \times 10^{24} \, kg$ and that of a natural satellite is $6.5 \times 10^{20} \, kg$. If the distance between them is $3.35 \times 10^{6} \, km$, calculate the force exerted by the Earth on it. $(G = 6.7 \times 10^{-11} \, Nm^{2} kg^{-2})$

$A$ stone is dropped from a cliff. Its speed after it has fallen $100 \,m$ is: (in $, m s^{-1}$)