# If an object with a mass of 5 kg  changes speed from 12m/s to  8m/s, by how much does its kinetic energy change?

Apr 6, 2016

$\Delta {E}_{k} = - 200 J$

#### Explanation:

$\text{data :}$
$m = 5 \text{ kg 'mass of object'}$
${v}_{i} = 12 \text{ m/s ' initial velocity of object'}$
${v}_{l} = 8 \text{ m/s 'final velocity of object'}$
${E}_{k} = \frac{1}{2} \cdot m \cdot {v}^{2} \text{ The kinetic energy of object}$

${E}_{i} = \frac{1}{2} \cdot 5 \cdot {12}^{2}$

${E}_{i} = \frac{5 \cdot 144}{2}$

${E}_{i} = 360 \text{ J the initial kinetic energy of object}$

${E}_{f} = \frac{1}{2} \cdot 5 \cdot {8}^{2}$

${E}_{f} = 5 \cdot \frac{64}{2}$

${E}_{f} = 160 \text{ J the final kinetic energy of object}$

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

$\Delta {E}_{k} = 160 - 360$

$\Delta {E}_{k} = - 200 J$