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I. Chapter Summary:

The chapter Work and Energy introduces two important physical quantities—work and energy, and their relationship with force and motion. It discusses conditions for work to be done, positive/negative/zero work, power and commercial units of energy, and types of mechanical energy—kinetic and potential. It also derives formulas related to work, energy, and power, and explores the Law of Conservation of Energy. The chapter connects physics to real-life examples like climbing stairs, running machines, and energy consumption.

II. Key Concepts Covered:

Concept	Description
Work	Done when a force causes displacement: W=F⋅d⋅cos⁡θW = F cdot d cdot costhetaW=F⋅d⋅cosθ
Positive/Negative/Zero Work	Depends on the angle between force and displacement
Kinetic Energy (K.E.)	Energy due to motion: KE=12mv2KE = frac{1}{2}mv^2KE=21​mv2
Potential Energy (P.E.)	Energy due to position: PE=mghPE = mghPE=mgh
Work-Energy Theorem	Work done = Change in kinetic energy
Power	Rate of doing work: P=WtP = frac{W}{t}P=tW​
Commercial Unit of Energy	1 kilowatt-hour (kWh) = 3.6 × 10⁶ joules
Law of Conservation of Energy	Energy can neither be created nor destroyed, only transformed

III. Important Questions:

(A) Multiple Choice Questions (1 Mark):

1. Which of the following is not a unit of work?
   a) joule
   b) erg
   c) newton ✅
   d) kWh
2. Work done is zero when:
   a) Object is displaced
   b) Force and displacement are perpendicular ✅
   c) Force is applied
   d) Object moves in direction of force
3. The commercial unit of energy is:
   a) Joule
   b) Erg
   c) kWh ✅
   d) Watt
4. The SI unit of power is:
   a) Watt ✅
   b) Joule
   c) Newton
   d) kg·m/s²

(B) Short Answer Questions (2/3 Marks):

1. A boy pushes a wall but fails to move it. How much work is done? Why?
2. Define 1 joule of work.
3. A body of mass 2 kg is moving with velocity 4 m/s. Find its kinetic energy.
4. Define power and write its SI unit.
   – PYQ 2021

(C) Long Answer Questions (5 Marks):

1. Derive the expression for kinetic energy.
2. A pump lifts 1000 kg of water to a height of 10 m in 50 seconds. Calculate:
   a) Work done
   b) Power used
   – PYQ 2020
3. Explain the law of conservation of energy with an example.
4. Compare commercial and SI units of energy. Calculate energy consumed by a 500 W appliance used for 4 hours.
   – PYQ 2022

(D) HOTS (Higher Order Thinking Skills):

1. A man carries a bag on his head and walks on a horizontal road. Is work being done? Explain why or why not.
2. Two boys of same weight run up a staircase. One does it in 30 seconds, the other in 20 seconds. Who uses more power and why?

IV. Key Formulas/Concepts:

Formula	Meaning
W=F⋅d⋅cos⁡θW = F cdot d cdot costhetaW=F⋅d⋅cosθ	Work done
KE=12mv2KE = frac{1}{2}mv^2KE=21​mv2	Kinetic energy
PE=mghPE = mghPE=mgh	Potential energy
P=WtP = frac{W}{t}P=tW​	Power
1 kWh=3.6×106 J1 , text{kWh} = 3.6 times 10^6 , text{J}1kWh=3.6×106J	Energy unit conversion
Work-Energy Theorem: W=ΔKEtext{Work-Energy Theorem: } W = Delta KEWork-Energy Theorem: W=ΔKE	Work is change in kinetic energy

V. Deleted Portions (CBSE 2025–2026):

 No portions have been deleted from this chapter as per the rationalized NCERT textbooks.

VI. Chapter-Wise Marks Bifurcation (Estimated – CBSE 2025–2026):

Unit/Chapter	Estimated Marks	Question Types Typically Asked
Work and Energy	7–9 marks	Numericals, derivations, concept-based short and long answers

VII. Previous Year Questions (PYQs):

Year	Marks	Question
2019	3	Define potential energy. Derive the formula.
2020	5	Derive KE formula. Explain conservation of energy.
2021	2	Define 1 kWh. Convert it to joules.
2022	3	Give an example where work done is negative. Explain.

VIII. Real-World Application Examples to Connect with Topics:

Concept	Application
Work	Lifting weights, towing cars, climbing stairs
Kinetic Energy	Running, moving vehicles, wind turbines
Potential Energy	Dams (stored water), roller coasters, springs
Power	Electrical bills, engine performance
Conservation of Energy	Pendulums, playground swings, hydroelectric dams

IX. Student Tips & Strategies for Success:

 Time Management:

• Spend alternate days solving numericals and revising concepts.
• Use unit charts for quick recall (Joule, Watt, kWh, etc.).

 Exam Preparation:

• Derivation of KE and SI vs. commercial units are frequently asked.
• Solve 5–10 numericals per day from reference books.
• Use diagrams to explain energy transformation.

 Stress Management:

• Visualize energy transformation using simple animations or real-life objects (spring, swing).
• Practice with group quizzes for fun-based revision.

X. Career Guidance & Exploration (Class-Specific):

For Classes 9–10:

Stream	Career Paths
Physics	Energy Analyst, Mechanical Physicist
Engineering	Power Systems Engineer, Renewable Energy Technician
Applied Science	Environmental Consultant, Energy Auditor

Entry Platforms:

• NTSE
• NSO
• CBSE Science Challenge
• DIY Energy Projects at school exhibitions

XI. Important Notes:

•  Learn the difference between mass and weight, power and energy.
•  Use SI units unless mentioned otherwise.
•  Practice derivations and unit conversions thoroughly.
•  Solve PYQs and HOTS regularly to build application-based thinking.