# What is the kinetic energy of an object with a mass of 9 kg that has been in freefall for 3 s?

Jan 17, 2016

First step is to find the velocity, which is $29.4 m {s}^{1}$, then use that to calculate the kinetic energy, $3889.6 J$.

#### Explanation:

The object starts at rest, so $u = 0 m {s}^{-} 1$ at $t = 0$. To find the velocity at $t = 3$ after accelerating at $a$, the acceleration due to gravity, $9.8 m {s}^{-} 2$:

$v = u + a t = 0 + 9.8 \cdot 3 = 29.4 m {s}^{-} 1$

The kinetic energy is given by:

${E}_{k} = \frac{1}{2} m {v}^{2} = \frac{1}{2} \cdot 9 \cdot {29.4}^{2} = 3889.6 J$