Work and energy are among the most important concepts in Physics because they explain how forces produce motion and how energy is transferred or transformed from one form to another. In Class 9 Physics Chapter 6, students learn the meaning of work, different forms of energy, the law of conservation of energy, power, efficiency, and the importance of renewable and non-renewable energy resources. These concepts are used in everyday life, from lifting objects and operating machines to generating electricity from natural resources.
Understanding this chapter helps students build a strong foundation for higher-level Physics and prepares them for school examinations, board exams, and entry tests. Instead of simply memorizing formulas, students should understand how work, energy, and power are related and how they are applied in real-life situations.
On this page, you’ll find solved Class 9 Physics Chapter 6 MCQs along with a quick chapter summary, important definitions, exam tips, frequently asked questions, and links to related Physics chapters. Practice these questions regularly to improve your conceptual understanding and perform confidently in examinations.
Learning Outcomes
After completing this chapter, students should be able to:
- Define work, energy, power, and efficiency.
- Explain the relationship between work and energy.
- Differentiate between kinetic and potential energy.
- Apply formulas related to work, power, and efficiency.
- Understand the importance of renewable and non-renewable energy resources.
- Solve numerical and conceptual questions based on work and energy.
Quick Notes – Chapter Summary
- Work is done when a force causes an object to move in the direction of the applied force.
- The SI unit of work is the joule (J).
- Energy is the ability to do work.
- Kinetic energy is the energy possessed by a moving object.
- Potential energy is the energy stored due to an object’s position or height.
- The work-energy principle states that the net work done on an object equals the change in its kinetic energy.
- Power is the rate at which work is done.
- The SI unit of power is the watt (W).
- Efficiency shows how effectively input energy is converted into useful output energy.
- Renewable energy resources include solar, wind, hydropower, and geothermal energy.
- Non-renewable resources include coal, petroleum, and natural gas.
- Energy cannot be created or destroyed; it only changes from one form to another.
Important Definitions
Work: The product of force and displacement in the direction of the applied force.
Energy: The capacity to do work.
Kinetic Energy: Energy possessed by an object because of its motion.
Potential Energy: Energy stored in an object due to its position or height.
Power: The rate of doing work or transferring energy.
Efficiency: The percentage of input energy converted into useful output energy.
Renewable Energy: Energy obtained from natural sources that are continuously replenished.
Non-Renewable Energy: Energy obtained from resources that are limited and take millions of years to form.
Important Formulas
Work = Force × Displacement => W = F × d
Power = Work / Time => P = W / t
Kinetic Energy = ½mv²
Potential Energy =mgh
Efficiency = (Useful Output Energy / Total Input Energy) × 100%
Multiple Choice Questions
1. Work is said to be done when:
- A. A force is applied and displacement occurs ✅
- B. A force is applied without displacement
- C. Displacement occurs without force
- D. Energy remains constant
Explanation: Work is done when a force moves an object in the direction of the force.
2. The SI unit of work is:
- A. Joule ✅
- B. Newton
- C. Watt
- D. Meter
Explanation: One joule is the work done when a force of one newton moves an object one meter.
3. Power is defined as:
- A. Work done per unit time ✅
- B. Force × distance
- C. Energy stored
- D. Force per unit area
Explanation: Power measures how quickly work is done, in watts.
4. The SI unit of power is:
- A. Watt ✅
- B. Joule
- C. Newton
- D. Volt
Explanation: One watt is equal to one joule per second.
5. Which energy is due to motion?
- A. Kinetic energy ✅
- B. Potential energy
- C. Chemical energy
- D. Nuclear energy
Explanation: Kinetic energy is the energy of a moving object.
6. Potential energy depends on:
- A. Height and mass ✅
- B. Velocity only
- C. Temperature
- D. Pressure
Explanation: Potential energy = mgh, where m is mass, g is gravity, and h is height.
7. The work-energy principle states that:
- A. Work done equals change in kinetic energy ✅
- B. Work equals power × time
- C. Energy can be created
- D. Force equals work × time
Explanation: The net work done on an object changes its kinetic energy.
8. Renewable energy source is:
- A. Solar energy ✅
- B. Coal
- C. Natural gas
- D. Petroleum
Explanation: Solar energy is renewable and sustainable.
9. Non-renewable energy source is:
- A. Coal ✅
- B. Wind energy
- C. Solar energy
- D. Hydropower
Explanation: Coal is finite and cannot be replenished in a short time.
10. Efficiency is given by the formula:
- A. (Useful energy output ÷ Total energy input) × 100% ✅
- B. Work ÷ Power
- C. Force × distance
- D. Power × time
Explanation: Efficiency measures how much input energy is converted to useful work.
11. Hydroelectric power is generated by:
- A. Falling water ✅
- B. Burning fuel
- C. Nuclear reactions
- D. Wind turbines
Explanation: Hydroelectric dams convert the potential energy of water into electricity.
12. Which form of energy is stored in food and fuel?
- A. Chemical energy ✅
- B. Thermal energy
- C. Mechanical energy
- D. Sound energy
Explanation: Chemical energy is released during chemical reactions.
13. 1 kilowatt-hour is equal to:
- A. 3.6 × 10⁶ joules ✅
- B. 1000 joules
- C. 360 joules
- D. 3600 joules
Explanation: 1 kWh is the energy used by a 1 kW appliance in 1 hour.
14. Geothermal energy is obtained from:
- A. Heat inside the Earth ✅
- B. Sunlight
- C. Wind
- D. Oceans
Explanation: Geothermal plants use heat from Earth’s interior to produce electricity.
15. Which factor does NOT affect the amount of work done?
- A. Color of the object ✅
- B. Force applied
- C. Displacement
- D. Direction of force
Explanation: Work depends on force, displacement, and angle between them, not color.
Exam Tips
– Memorize the SI units of work, energy, and power.
– Learn the formulas for work, power, kinetic energy, potential energy, and efficiency.
– Understand the difference between kinetic and potential energy.
– Practice numerical problems involving work and power.
– Revise renewable and non-renewable energy resources before the exam.
Common Mistakes Students Make
❌ Confusing work with force.
❌ Forgetting that work requires displacement.
❌ Mixing up kinetic and potential energy.
❌ Using incorrect SI units in numerical problems.
❌ Forgetting to convert kilowatt-hours into joules.
Conclusion
Understanding work and energy is essential for solving many Physics problems and for explaining how machines, vehicles, and natural systems operate. Regular practice of these MCQs, along with revising the important definitions and formulas, will strengthen your concepts and help you perform well in school examinations and board exams.