Work, Energy, and Power – Class 11 Physics NCERT | Formulas, Derivations & Examples

⚡ Work, Energy, and Power – Class 11 Physics (NCERT)

This chapter from Class 11 Physics NCERT explains the basic concepts of Work, different forms of Energy, and the concept of Power. These are foundational ideas used in all branches of physics.

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🧱 What is Work?

Work is said to be done when a force is applied on a body and there is displacement in the direction of the force.

Work (W) = F × d × cosθ

• F = Force
• d = Displacement
• θ = Angle between force and displacement

✅ Types of Work

• Positive Work → θ < 90°
• Negative Work → θ > 90°
• Zero Work → θ = 90° (e.g., circular motion)

SI Unit: Joule (J)

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🔋 What is Energy?

Energy is the capacity to do work. It exists in various forms: mechanical, thermal, chemical, electrical, etc.

🔹 Kinetic Energy (K.E.)

Energy possessed by a body due to motion.

K.E. = ½mv²

🔹 Potential Energy (P.E.)

Energy possessed due to position or configuration.

P.E. = mgh

Total Mechanical Energy = K.E. + P.E. (conserved in absence of friction)

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📉 Work-Energy Theorem

Statement: The net work done by the force on an object is equal to the change in its kinetic energy.

W_net = ΔK.E. = ½mv² – ½mu²

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⚙️ What is Power?

Power is the rate of doing work or the rate of transfer of energy.

Power (P) = Work / Time

• SI Unit: Watt (W)
• 1 kilowatt (kW) = 1000 watts

💡 Commercial Unit of Energy:

1 kWh = 3.6 × 10⁶ Joules

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📋 Summary Table

Concept	Formula	Unit
Work	W = F × d × cosθ	Joule (J)
Kinetic Energy	K.E. = ½mv²	Joule (J)
Potential Energy	P.E. = mgh	Joule (J)
Power	P = Work / Time	Watt (W)
1 kWh	1 kWh = 3.6 × 10⁶ J	Energy Unit

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📌 Real-Life Applications

• Horsepower of vehicles (1 HP = 746 W)
• Electric bills calculated in kWh
• Gravitational energy in dams and water tanks

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Tags: Work Energy Power, Class 11 Physics, NCERT Notes, CBSE Physics, Kinetic Energy, Potential Energy, Power Formula, Science Blog