# If an object with a mass of 15 kg  changes speed from 8 m/s to 14 m/s, by how much does its kinetic energy change?

I found a change of $\Delta K = 990 J$.
Kinetic Energy $K$ is given as:
$K = \frac{1}{2} m {v}^{2}$
Considering the initial and final stages of your phenomenon you have that the change in $K$ will be:
$\Delta K = {K}_{f} - {K}_{i} = \frac{1}{2} m {v}_{f}^{2} - \frac{1}{2} m {v}_{i}^{2} = \frac{1}{2} m \left({v}_{f}^{2} - {v}_{i}^{2}\right) =$
$= \frac{1}{2} \cdot 15 \cdot \left({14}^{2} - {8}^{2}\right) = 990 J$