Work, Energy and Power - Class 11 Physics

Work, Energy and Power

1. Work

Work is said to be done when a force is applied and the object is displaced in the direction of force.
Work is a scalar quantity.
Formula: W = F · d · cos(θ)
Where:
- W = Work done (in joules)
- F = Magnitude of the applied force (in newtons)
- d = Displacement of the object (in meters)
- θ = Angle between force and displacement
Units: SI Unit is Joule (J)
Types of Work:
- Positive Work (0° ≤ θ < 90°)
- Negative Work (90° < θ ≤ 180°)
- Zero Work (θ = 90°)

Energy is the capacity of a body to do work.
It is a scalar quantity.
SI Unit: Joule (J)
Types of Energy:
- Kinetic Energy (KE) – due to motion
- Potential Energy (PE) – due to position or configuration
Formulas:

Kinetic Energy: KE = 1/2 · m · v²
Potential Energy: PE = m · g · h
Where:
- m = mass of object (kg)
- v = velocity (m/s)
- g = acceleration due to gravity (9.8 m/s²)
- h = height (m)

This theorem states that the work done by all forces acting on a particle equals the change in its kinetic energy.
Formula: W = ΔKE = KE_final - KE_initial
This is a powerful tool for solving motion problems without using kinematic equations.

Power is the rate of doing work or the rate of transfer of energy.
Formula: P = W / t
Where:
- P = Power (watts)
- W = Work done (joules)
- t = Time taken (seconds)
SI Unit: Watt (W)
Other units:
- 1 kilowatt (kW) = 1000 W
- 1 horsepower (HP) ≈ 746 W

Energy can neither be created nor destroyed, it can only change from one form to another.
Total energy of an isolated system remains constant.
Example: In a pendulum, energy converts between potential and kinetic energy continuously.