# If an object with a mass of 2 kg  changes speed from 9 m/s to 12 m/s, by how much does its kinetic energy change?

Jun 14, 2018

The change in kinetic energy is $= 63 J$

#### Explanation:

The kinetic enegy is

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

The change in kinetic energy is

$\Delta K E = \frac{1}{2} m {v}^{2} - \frac{1}{2} {\mu}^{2} = \frac{1}{2} m \left({v}^{2} - {u}^{2}\right)$

The mass is $m = 2 k g$

The initial speed is $u = 9 m {s}^{-} 1$

The final speed is $v = 12 m {s}^{-} 1$

The cgange in kinetic energy is

$\Delta K E = \frac{1}{2} \cdot 2 \cdot \left({12}^{2} - {9}^{2}\right) = 63 J$