# If an object with a mass of 5 kg  changes speed from 4m/s to  7m/s, by how much does its kinetic energy change?

##### 2 Answers

Change in KE$= 82.5 \text{ }$joule

#### Explanation:

Given ${v}_{f} = 7 \text{ }$m/sec and ${v}_{0} = 4 \text{ }$m/sec
and mass $m = 5 \text{ }$kg

Formula for Kinetic Energy :

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

Change in KE$= \frac{1}{2} \cdot m {v}_{f}^{2} - \frac{1}{2} \cdot m {v}_{0}^{2}$

Change in KE$= \frac{1}{2} \cdot m \cdot \left({v}_{f}^{2} - {v}_{0}^{2}\right)$

Change in KE$= \frac{1}{2} \cdot 5 \cdot \left({7}^{2} - {4}^{2}\right)$

Change in KE$= 82.5 \text{ }$joule

God bless....I hope the explanation is useful.

Apr 30, 2016

$= 82.5 J$

#### Explanation:

• Mass of the object $m = 5 k g$
• Initial velocity ${v}_{i} = 4 \frac{m}{s}$
• Initial velocity ${v}_{f} = 7 \frac{m}{s}$
• The change in KE =$\frac{1}{2} \times m \left({v}_{f}^{2} - {v}_{i}^{2}\right) = \frac{1}{2} \times 5 \times \left({7}^{2} - {4}^{2}\right) J$

$= 82.5 J$