SEBA Class 9 Science Important Chapter 11 Work and Energy

SEBA Class 9 Science Important Chapter 11 Work and Energy Solutions English Medium As Per SEBA New Syllabus to each chapter is provided in the list so that you can easily browse through different chapters SEBA Class 9 General Science Additional Solutions and select need one. NCERT Important Solutions For Class 9 General Science Download PDF. Important Notes for Class 9 Science.

SEBA Class 9 Science Important Chapter 11 Work and Energy

Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. Assam SEBA Board Class 9 Science Additional Question Answer are part of All Subject Solutions. Here we have given CBSE Class 9 Science Important Notes for All Chapters, You can practice these here.

Work and Energy

Chapter: 11

IMPORTANT QUESTION ANSWER

Answer the Following Question:

1. Define 1 joule of work.

Ans: 1 joule of work is said to be done when a force of 1 newton displaces an object by 1 metre in the direction of the force.

2. How is work done negative? Give an example.

Ans: Work is negative when the force acts in the opposite direction of displacement. 

Example: Friction acting against motion.

3. Give two examples of situations where no work is done despite applying force.

Ans: (i) Pushing a wall that does not move.

(ii) Holding a heavy bag without moving.

4. What is the physical significance of energy?

Ans: Energy is the capacity to do work. It is essential for all physical activities and mechanical processes.

5. State the law of conservation of energy.

Ans: Energy can neither be created nor destroyed; it can only be transformed from one form to another. The total energy remains constant.

6. What happens to the energy of a freely falling body?

Ans: Its potential energy decreases while its kinetic energy increases. The total energy remains constant.

7. Define 1 kilowatt-hour. How many joules does it equal?

Ans: 1 kilowatt-hour is the energy consumed when 1000 W power is used for 1 hour.

1kWh = 1000 × 3600 = 3.6 × 106J

8. What is average power?

Ans: Average power is the total work done divided by the total time taken.

Average Power = Total Work/Total Time

9. A body of mass 5 kg is moving with velocity 2 m/s. Find its kinetic energy.

Ans: K.E.= 1/2mv² = ½ × 5 × 2² = 10 J

10. Why is energy needed? Give two uses.

Ans: Energy is needed to perform daily life activities and run machines.

Uses: (i) Running household appliances.

(ii) Moving vehicles.

11. Define commercial unit of energy. How does it differ from SI unit of energy?

Ans: Commercial unit: Kilowatt-hour (kWh), used for electricity bills.

SI unit: Joule (J)

Difference: 1kWh = 3.6 × 10⁶J

12. An electric motor lifts 100 kg of water to a height of 20 m in 5 seconds. Find the power used and energy consumed.

Ans: Given: m = 100 kg, h = 20 m,t = 5 s,g = 10 m/s²

Work done = mgh = 100 × 10 × 20 = 20000 J

Power = 20000/5 = 4000W = 4kW

13. Explain why work done is zero when a person carries a load and walks on a flat road.

Ans: Though the person applies upward force (to balance weight), displacement is horizontal. Since force is perpendicular to displacement, Work done = 0

14. List two conditions when mechanical energy of a body remains conserved.

Ans: Mechanical energy (K.E. + P.E.) is conserved when:

(i) No external force acts (like friction or air resistance)

(ii) The system is isolated (e.g., in free fall under gravity).

15. What is meant by mechanical energy? Name its two forms.

Ans: Mechanical energy is the energy possessed by a body due to its motion or position.

Its two forms are:

(i) Kinetic Energy (K.E.) – due to motion

(ii) Potential Energy (P.E.) – due to position