# What is the kinetic energy of an object with a mass of 5 kg that has been in freefall for 8 s?

Feb 5, 2016

$15.366 k J$

#### Explanation:

Assuming the object has fallen from rest near earth, we may use the equations of motion for constant acceleration to find its velocity after 8 seconds :

$v = u + a t$

$= 0 + \left(9 , 8\right) \left(8\right)$

$= 78 , 4 m / s$

Hence its kinetic energy at this stage is

${E}_{k} = \frac{1}{2} m {v}^{2}$

$= \frac{1}{2} \times 5 \times {78.4}^{2}$

$= 15 , 366 k J$