# Amy drops a ball from an initial height of 30 feet above the ground. After how many seconds will the ball reach the ground?

Feb 28, 2017

I got $1.3 s$

#### Explanation:

I am not sure it is algebra but anyway...
I would use the general relationship from kinematics:

$h = {v}_{i} t + \frac{1}{2} a {t}^{2}$

where:
$h = 30 \text{ft} = 9.144 m \approx 9 m$
${v}_{i} = 0$ is the initial velocity;
t=? time;
$a = 9.8 \frac{m}{s} ^ 2$ is the acceleration of gravity.
We get:
$9 = 0 t + \frac{9.8}{2} {t}^{2}$
rearranging:
$t = \sqrt{\frac{18}{9.8}} = 1.3 s$