# What is the kinetic energy of an object with a mass of  16 kg that has been in freefall for  4 s?

##### 1 Answer
Mar 2, 2016

The kinetic ebergy will be ${E}_{k} = \frac{1}{2} m {v}^{2}$ with $m = 16 k g$

#### Explanation:

Now the speed $v$:
Acceleration of gravity $g = 9.81 m / {s}^{2}$
Which means that after $t = 4 s$ the velocity will be:
$v = g \times t = 9.81 \times 4 = 39.24 m / s$

Using this in the original formula we get:

${E}_{k} = \frac{1}{2} \times 16 \times {\left(39.24\right)}^{2} = 12318 J \approx 12.3 k J$