If an object with a mass of  3kg  changes speed from 5m/s to  9m/s, by how much does its kinetic energy change?

$\Delta K E = 84 \text{ }$Joules

Explanation:

Given data:
$m = 3 \text{ }$kg
${v}_{i} = 5 \text{ }$m/sec
${v}_{f} = 9 \text{ }$m/sec

$\Delta K E = K {E}_{f} - K {E}_{i}$

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

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

$\Delta K E = \frac{1}{2} \left(3\right) \cdot \left({9}^{2} - {5}^{2}\right)$

$\Delta K E = \frac{1}{2} \left(3\right) \cdot \left(81 - 25\right)$

$\Delta K E = \frac{1}{2} \left(3\right) \cdot \left(56\right)$

$\Delta K E = 84 \text{ }$Joules

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