# Question #35de3

Sep 26, 2016

$2.71 s$, rounded to two decimal places.

#### Explanation:

Free fall under gravity is governed by the kinematic equation
$h = u t + \frac{1}{2} g {t}^{2}$
Where $h$ is height from which body starts falling,
$u$ is its initial velocity
$g$ is acceleration due to gravity and is $9.81 m {s}^{-} 2$
and $t$ is the time taken for the fall to reach ground level.

In this question we take ground level as the sea level. Inserting given quantities we get
$36 = 0 \times t + \frac{1}{2} \times 9.81 \times {t}^{2}$
$\implies \frac{1}{2} \times 9.81 \times {t}^{2} = 36$
$\implies {t}^{2} = \frac{36 \times 2}{9.81}$
$\implies t = \sqrt{\frac{36 \times 2}{9.81}}$
$\implies t = \pm 2.71$, rounded to two decimal places.
ignoring the $- v e$ root as time can not be negative
$t = 2.71 s$