Originally Posted by

**Cthul** Given that a ball is thrown vertically up.

The ball reaches $\displaystyle 78.4\text{m}$ as a maximum height. (Gravity is 9.8)

Find the total time the ball was in the air.

The information given is:

$\displaystyle

a=9.8\text{m}\text{s}^{\text{-}2}

$ Mr F says: If you want s = 78.4, then a = -9.8, not 9.8. s and a are vectors and in straight line motion direction is specified by + or -.

$\displaystyle

s=78.4\text{m}

$

$\displaystyle

u=39.2\text{m}\text{s}^{\text{-}1}$ (I worked out the initial speed, it's correct)

$\displaystyle

v=0{m}\text{s}^{\text{-}1}

$

$\displaystyle

t=x

$

For the ball going up only.

How do I find the rest of the time?