An object thrown vertically upwards reaches a height of $500 \mathrm{m}$. What was its initial velocity (in $\mathrm{m} {\mathrm{s}}^{-1}$)? $\left(g=10 \mathrm{m} {\mathrm{s}}^{-2}\right)$

A metal ball of mass $5 \mathrm{kg}$ falls from a height of$490 \mathrm{m}$. How much time it will take to reach the ground?$(g = 9.8 \mathrm{m}/{\mathrm{s}}^2)$

The value of $g$ at the centre of the Earth is _____.

(Choose from: infinity/ zero) 

A ball thrown up vertically returns to the thrower after 6 s. (Use g = $10 \mathrm{m}/{\mathrm{s}}^2$)Find
(a) the velocity with which it was thrown up,
(b) the maximum height it reaches, and
(c) its position after 4 s.