# If an object with a mass of 2 kg  changes speed from 6 m/s to 2 m/s, by how much does its kinetic energy change?

May 13, 2018

So the kinetic energy was reduced by a factor of $4$. Or, equivalently, the kinetic energy was reduced by $27 \text{J}$.

#### Explanation:

Before:

${E}_{k} = \frac{1}{2} m {v}_{i}^{2} = \frac{1}{2} \left(2\right) {\left(6\right)}^{2} = 36 \text{ J}$

After:

${E}_{k} = \frac{1}{2} m {v}_{f}^{2} = \frac{1}{2} \left(2\right) {\left(3\right)}^{2} = 9 \text{ J}$

So the kinetic energy was reduced by a factor of $4$. Or, equivalently, the kinetic energy was reduced by $27 \text{J}$.