# If an object with a mass of 7 kg  changes speed from 3 m/s to 8m/s, by how much did its kinetic energy change by?

Jan 10, 2016

I found: $\Delta K = 192.5 J$

#### Explanation:

You know that kinetic energy is given as:
$K = \frac{1}{2} m {v}^{2}$

So the change in kinetic energy will be:

$\Delta K = \frac{1}{2} m {v}_{f}^{2} - \frac{1}{2} m {v}_{i}^{2} =$

$= \frac{1}{2} m \left({v}_{f}^{2} - {v}_{i}^{2}\right) =$

$= \frac{1}{2} \cdot 7 \cdot \left({8}^{2} - {3}^{2}\right) = \frac{7}{2} \left(64 - 9\right) = 192.5 J$