Work, Energy and Power
Subject: Physics | Topic: Work, Energy and Power
For TLT, ECT, PST, JEST & All Competitive Exams
Whether lifting a bag, running, or switching on a bulb, three Physics concepts are always at work — Work, Energy, and Power. These three ideas are closely linked, and together they explain how forces cause motion and how that motion is measured. This topic is a core, frequently tested area of Physics in TLT, ECT, PST, and JEST exams.
Work
In Physics, Work is done when a force causes an object to move in the direction of the force. If there is no movement, no work is done, no matter how much force is applied. Its SI unit is the Joule (J).
(Work = Force × Distance moved in the direction of force)
Energy
Energy is the capacity to do work. Like work, its SI unit is also the Joule (J). Energy exists in many forms, but the two most important mechanical forms are Kinetic Energy and Potential Energy.
Kinetic Energy (KE)
Kinetic Energy is the energy possessed by an object due to its motion.
(m = mass, v = velocity)
Potential Energy (PE)
Potential Energy is the energy possessed by an object due to its position or height.
(m = mass, g = gravitational acceleration, h = height)
Kinetic and Potential Energy in a Falling Ball
Law of Conservation of Energy
This law states that energy can neither be created nor destroyed — it can only be transformed from one form to another. The total energy of an isolated system always remains constant.
Power
Power is the rate of doing work, or the rate at which energy is transferred. Its SI unit is the Watt (W).
(Power = Work Done / Time Taken)
Solved Examples
Example 1: Finding Work Done
A force of 20 N moves an object a distance of 5 m. Find the work done.
Solution: W = F × d = 20 × 5 = 100 J
Example 2: Finding Kinetic Energy
A 2 kg object moves with a velocity of 3 m/s. Find its kinetic energy.
Solution: KE = ½ × m × v² = ½ × 2 × 3² = ½ × 2 × 9 = 9 J
Example 3: Finding Potential Energy
A 5 kg object is placed at a height of 2 m (g = 10 m/s²). Find its potential energy.
Solution: PE = m × g × h = 5 × 10 × 2 = 100 J
Example 4: Finding Power
A machine does 500 J of work in 10 seconds. Find its power.
Solution: P = W / t = 500 / 10 = 50 W
Why This Topic Matters
Work, Energy and Power are fundamental Physics concepts that connect directly to topics like Newton's Laws of Motion and Simple Machines studied earlier. Their clear formulas and numerical examples make this a high-scoring, frequently repeated topic in TLT, ECT, PST, and JEST exams.
Practice MCQs
1. What is the SI unit of Work and Energy?
a) Newton b) Watt c) Joule d) Ampere
2. What is the formula for Kinetic Energy?
a) KE = mgh b) KE = ½mv² c) KE = Fd d) KE = W/t
3. A force of 20 N moves an object a distance of 5 m. Find the work done.
a) 4 J b) 15 J c) 25 J d) 100 J
4. What does the Law of Conservation of Energy state?
a) Energy can be destroyed b) Energy can be created c) Energy can neither be created nor destroyed d) Energy always increases
5. What is the SI unit of Power?
a) Joule b) Newton c) Watt d) Volt
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