A stone thrown vertically upward takes $3 \text{s}$ to attain the maximum height. Calculate,

(i) the initial velocity of the stone.

(ii) the maximum height attained by the stone.

(Take $g=9.8 \raisebox{1ex}{$\mathrm{m}$}\!\left/ \!\raisebox{-1ex}{${\mathrm{s}}^2$}\right.$)

A stone thrown vertically upward returns to the thrower in $4 \mathrm{s}$ Calculate

(i) the initial velocity of the stone 

(ii) the maximum height attained by the stone. Take  $g=10 \mathrm{m} {\mathrm{s}}^{-2}$.

A ball thrown vertically upward rises to a height of $20 \mathrm{m}$. If the acceleration due to gravity is $10 \mathrm{m} {\mathrm{s}}^{-2}$. Calculate the initial velocity of the ball. (Take $g=10 \mathrm{m} {\mathrm{s}}^{-2}$)