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:
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Kinetic energy
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Nuclear energy
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Thermal energy
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Electrical energy
Kinetic Energy
Kinetic energy is the type of energy an object possesses when in motion.
Examples:
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A moving car has kinetic energy
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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)=21mv2
Where:
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m = mass of the object (kg)
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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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