Resources | Subject Notes | Physics
This section focuses on understanding and applying the concept of kinetic energy. We will learn the equation for kinetic energy and how to use it to solve problems.
Kinetic energy is the energy possessed by an object due to its motion. Any object that is moving has kinetic energy. The amount of kinetic energy an object has depends on its mass and its speed.
The kinetic energy (KE) of an object is calculated using the following equation:
$$KE = \frac{1}{2} m v^2$$Where:
This equation shows that kinetic energy is directly proportional to both mass and the square of the speed. This means that doubling the mass doubles the kinetic energy. And doubling the speed quadruples the kinetic energy.
To use the equation, you need to know the mass of the object and its speed. Make sure you use consistent units (kg for mass and m/s for speed). Here's an example:
Example: A ball with a mass of 0.2 kg is moving at a speed of 3 m/s. What is its kinetic energy?
Solution:
KE = $\frac{1}{2} \times m \times v^2$
KE = $\frac{1}{2} \times 0.2 \text{ kg} \times (3 \text{ m/s})^2$
KE = $\frac{1}{2} \times 0.2 \text{ kg} \times 9 \text{ m}^2/\text{s}^2$
KE = $0.9 \text{ J}$
Therefore, the kinetic energy of the ball is 0.9 Joules.
| Quantity | Symbol | Units |
|---|---|---|
| Kinetic Energy | KE | Joules (J) |
| Mass | m | Kilograms (kg) |
| Speed | v | Metres per second (m/s) |
It's crucial to remember that kinetic energy is a scalar quantity, meaning it only has magnitude and no direction. The direction of motion is not relevant when calculating kinetic energy.
Also, the equation KE = $\frac{1}{2} m v^2$ applies to objects moving in a straight line. For objects moving in curved paths, other forms of energy (like potential energy) are also involved.