Energy

In simple terms, energy is the ability to do some work — for example, lifting a glass of water or holding a cricket bat.

It is the capacity to do work.
The unit of energy is measured in joules (J).

There are many sorts of energy. Some main kinds are:

• Kinetic energy

• Nuclear energy

• Thermal energy

• Electrical energy

Kinetic Energy

Kinetic energy is the type of energy an object possesses when in motion.

Examples:

• A moving car has kinetic energy

• A cricket ball flying through the air has kinetic energy

Equation for Kinetic Energy

Kinetic Energy (KE)=12mv2\text{Kinetic Energy (KE)} = \frac{1}{2} m v^2Kinetic Energy (KE)=21​mv2

Where:

• m = mass of the object (kg)

• v = velocity of the object (m/s)

Examples

Example 1:
Ball moving with velocity 6 m/s6 \, m/s6m/s, mass = 2 kg2 \, kg2kg

KE=12×2×62=36 joulesKE = \frac{1}{2} \times 2 \times 6^2 = 36 \, \text{joules}KE=21​×2×62=36joules

Example 2:
Knife moving with velocity 5 m/s5 \, m/s5m/s, mass = 1 kg1 \, kg1kg

KE=12×1×52=12.5 joulesKE = \frac{1}{2} \times 1 \times 5^2 = 12.5 \, \text{joules}KE=21​×1×52=12.5joules

Example 3:
Plane moving with velocity 100 m/s100 \, m/s100m/s, mass = 2000 kg2000 \, kg2000kg

KE=12×2000×1002=100,000,000 joulesKE = \frac{1}{2} \times 2000 \times 100^2 = 100{,}000{,}000 \, \text{joules}KE=21​×2000×1002=100,000,000joules

Example 4:
Boy moving with velocity 9 m/s9 \, m/s9m/s, mass = 60 kg60 \, kg60kg

KE=12×60×92=2430 joulesKE = \frac{1}{2} \times 60 \times 9^2 = 2430 \, \text{joules}KE=21​×60×92=2430joules

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