Work, Energy and Power
Subject: Physics | Topic: Work, Energy and Power
For TLT, ECT, PST, JEST & All Competitive Exams
Whether it's lifting a bag, a car climbing a hill, or a bulb glowing, all of these involve work, energy, and power — three of the most fundamental and closely related concepts in Physics. This topic is a regular part of General Science/Physics and is frequently tested in ECT, BPS-15, PST, JEST, and other competitive exams.
What is Work?
In Physics, work is said to be done when a force is applied on an object and the object moves in the direction of the force. Work is calculated using the formula:
The SI unit of work is the Joule (J).
If a force is applied but the object does not move, no work is done in the physics sense — even if a person feels tired from pushing.
What is Energy?
Energy is the capacity or ability to do work. Anything that can do work possesses energy. Like work, energy is also measured in Joules (J). Energy exists in many forms, such as mechanical, heat, light, sound, chemical, and electrical energy, and it can change from one form to another, but it can never be created or destroyed — this is known as the Law of Conservation of Energy.
Types of Mechanical Energy
Kinetic Energy
Kinetic energy is the energy possessed by an object due to its motion. Any moving object — a rolling ball, a flying bird, a moving car — has kinetic energy. It is calculated using:
Where m = mass of the object, v = velocity of the object
The faster an object moves, or the greater its mass, the more kinetic energy it has.
Potential Energy
Potential energy is the energy stored in an object due to its position or state. A common form is gravitational potential energy, which depends on an object's height above the ground. It is calculated using:
Where m = mass, g = acceleration due to gravity, h = height
Examples of potential energy include a stretched rubber band, water stored in a dam, or a book placed on a high shelf.
What is Power?
Power is the rate at which work is done, or the rate at which energy is transferred or converted. It tells us how quickly work is being performed. Power is calculated as:
The SI unit of power is the Watt (W).
A more powerful machine does the same amount of work in less time compared to a less powerful one.
Work, Energy and Power at a Glance
| Concept | Formula | SI Unit |
|---|---|---|
| Work | W = F × d | Joule (J) |
| Kinetic Energy | KE = ½ × m × v² | Joule (J) |
| Potential Energy | PE = m × g × h | Joule (J) |
| Power | P = W ÷ t | Watt (W) |
Why Work, Energy and Power Matter
These concepts form the backbone of mechanics and are directly connected to Newton's Laws of Motion. They explain how machines, vehicles, and even the human body perform tasks, and they help engineers design efficient systems — from electrical appliances rated in watts to vehicles rated by horsepower. Understanding work, energy, and power is essential for grasping how energy flows and transforms in the physical world.
Practice MCQs
1. What is the SI unit of work?
a) Watt b) Joule c) Newton d) Pascal
2. What is the formula for kinetic energy?
a) KE = m × g × h b) KE = F × d c) KE = ½ × m × v² d) KE = W ÷ t
3. What is potential energy?
a) Energy due to motion b) Energy stored due to position or state c) Energy lost as heat d) Energy of sound
4. What is the SI unit of power?
a) Joule b) Newton c) Watt d) Pascal
5. Power is defined as:
a) Force × Distance b) Work ÷ Time c) Mass × Velocity d) Mass × Gravity × Height
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