# Thread: [Kinematics] Total time in air

1. ## [Kinematics] Total time in air

Given that a ball is thrown vertically up.
The ball reaches $78.4\text{m}$ as a maximum height. (Gravity is 9.8)

Find the total time the ball was in the air.
The information given is:
$
a=9.8\text{m}\text{s}^{\text{-}2}
$

$
s=78.4\text{m}
$

$
u=39.2\text{m}\text{s}^{\text{-}1}$
(I worked out the initial speed, it's correct)
$
v=0{m}\text{s}^{\text{-}1}
$

$
t=x
$

For the ball going up only.

How do I find the rest of the time?

2. Originally Posted by Cthul
Given that a ball is thrown vertically up.
The ball reaches $78.4\text{m}$ as a maximum height. (Gravity is 9.8)

Find the total time the ball was in the air.
The information given is:
$
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 -.

$
s=78.4\text{m}
$

$
u=39.2\text{m}\text{s}^{\text{-}1}$
(I worked out the initial speed, it's correct)
$
v=0{m}\text{s}^{\text{-}1}
$

$
t=x
$

For the ball going up only.

How do I find the rest of the time?
In the absence of air resistance, time up = time down.

3. I can't believe that was so easy. Thanks.