Work, Energy and power

Class 9th Physics Chapter 5

Work, Energy and Power

Work and Energy is an important concept in the physics field.
In this chapter, we discuss the work, energy and power.
Work
Work is defined as the product of magnitude of force and the
distance covered in the direction of force.
𝑤𝑜𝑟𝑘 𝑑𝑜𝑛𝑒 = 𝐹𝑜𝑟𝑐𝑒 x 𝐷𝑖𝑠𝑝𝑙𝑎𝑐𝑒𝑚𝑒𝑛𝑡
Therefore,
W=FxD
If the force is making the angle 𝜃 with the
displacement and the component of force
F cos 𝜃
𝑊 = 𝐹𝑑 cos 𝜃
The SI unit of the work is joule (J).
Energy
Energy is can be defined as the ability to do work.
When one joule work is done on the body, the amount of energy
spent is one joule.
Type of Energy
➢ Kinetic Energy
➢ Potential Energy

, Therefore, the combination of these two types of energy is called
mechanical energy.
Kinetic Energy
Kinetic energy is a possessed by an object due to its motion.
1
𝐾𝐸 = 𝑚𝑣 2
2
The SI unit is Joule.
Potential Energy
Potential energy is the stored energy
possessed by an object because of its position, shape, or condition.
The SI unit is Joule.
𝑃𝐸 = 𝑚𝑔ℎ


Conservation of Energy
Energy cannot be destroyed or created, but it can transfer from one
to another amount but the total amount of energy never changes.
Derivation
Using the equation of motion
𝑣 2 = 𝑢2 + 2𝑔ℎ
The object starts from rest
𝑢=0
Therefore,
𝑣 2 = 2𝑔ℎ