Work and Energy Class 9 Science Chapter 10 Important Questions is very important because it teaches basic ideas that are used in physics and in everyday life.
This chapter helps students understand what work and energy are, and how they are connected. Studying this chapter not only helps in exams but also prepares students for more advanced science topics. By practicing these questions students can improve their understanding and problem-solving skills.
Important Questions Class 9 Science Chapter 10 Work and Energy
Here we have provided Work and Energy- chapter 9 science class 10 important questions below:
Very Short Answer Questions
1. A body of mass 2 kg is raised to a height of 1 m. Find the work done by the force of gravity.
(A) 19.6 J
(B) –19.6 J
(C) Zero
(D) None of these
Ans. (B)
2. From the graph of Force versus displacement of a particle, find the total work done by the force.
Ans:
Options:
(A) 90 J
(B) 30 J
(C) 180 J
(D) 60 J
Ans. (A)
3. A force displaces a 5 kg body to 10 m in 10 sec and its velocity becomes 20 m/s. Calculate the power delivered.
(A) 10 W
(B) 20 W
(C) 40 W
(D) 100 W
Ans. (A)
4. In case of negative work, the angle between the force and displacement is:
(A) 0°
(B) 45°
(C) 90°
(D) 180°
Ans. (D)
5. A car is accelerated on a leveled road and attains a speed of 4 times its initial speed. In this process, the kinetic energy of the car:
(A) Does not change
(B) Becomes 4 times that of initial kinetic energy
(C) Becomes 8 times that of initial kinetic energy
(D) Becomes 16 times that of initial kinetic energy
Ans. (D)
6. The energy possessed by a body by virtue of its motion is called:
(A) Potential energy
(B) Kinetic energy
(C) Attractive energy
(D) Gravitational energy
Ans. (B)
7. The energy used in one hour at the rate of 1 kW is known as:
(A) 10 kWh
(B) 1 kWh
(C) 1 W
(D) 1 km h
Ans. (B)
8. Various factors affecting kinetic energy are:
(A) Mass
(B) Momentum
(C) Velocity
(D) All the above
Ans. (D)
9. The power of a pump which can pump 200 kg of water to a height of 200 m in 10 s is: (g = 10 m/s²)
(A) 40 kW
(B) 80 kW
(C) 4000 kW
(D) 960 kW
Ans. (A)
10. Which one of the following is not the unit of energy?
(A) Joule
(B) Newton metre
(C) Kilowatt
(D) Kilowatt hour
Ans. (C)
11. Assertion–Reason
Assertion: Kinetic energy of a body is quadrupled when its velocity is doubled.
Reason: Kinetic energy is proportional to the square of velocity.
(A) Both A and R are true, and R is the correct explanation of A
(B) Both A and R are true but R is not the correct explanation
(C) A is true but R is false
(D) A is false but R is true
Ans. (A)
12. Assertion–Reason
Assertion: An object increases its energy when raised through a height.
Reason: Work is done on it against gravity while raising.
(A) Both A and R are true and R explains A
(B) Both A and R are true but R does not explain A
(C) A true but R false
(D) A false but R true
Ans. (A)
13. Assertion–Reason
Assertion: The sum of kinetic energy and potential energy of an object is its mechanical energy.
Reason: The sum of PE and KE would not be the same at all points.
(A) Both A and R true and R explains A
(B) Both true but R doesn’t explain
(C) A true but R false
(D) A false but R true
Ans. (C)
14. Assertion–Reason
Assertion: Kinetic energy of a body can be negative.
Reason: When a body rolls down an inclined plane, it has both kinetic and potential energy.
(A) Both A and R true and R explains A
(B) Both A and R true but R doesn't explain
(C) A true but R false
(D) A false but R true
Ans. (D)
15. Assertion–Reason
Assertion: A more powerful vehicle completes a journey in shorter time than a less powerful one.
Reason: Power measures the speed of doing work.
(A) Both A and R true and R explains A
(B) Both true but R doesn't explain
(C) A true but R false
(D) A false but R true
Ans. (A)
16. A rocket is moving up with velocity v. If the velocity is tripled, what will be the ratio of kinetic energies?
17. What are the various energy transformations when riding a bicycle?
Solution:
Muscular Energy → Kinetic Energy + Heat Energy
Total energy remains conserved.
18. A body performs no work. Does it imply that the body possesses no energy?
Solution:
No. A body may possess energy even without doing work.
Example: A book on a table has potential energy.
19. Swaralee takes 20 s to carry a 20 kg bag to a height of 5 m. How much power has she used?
Given:
m = 20 kg, h = 5 m, t = 40 s
Force applied = mg = 196 N
Work done = F × s = 196 × 5 = 980 J
20. “If a satellite revolves around the earth in a circular orbit, the amount of work done is zero.” Justify.
Solution:
Force of gravity acts towards centre → displacement is tangential.
Angle between force and displacement = 90°
21. (i) Can a body possess energy without momentum?
(ii) Can it possess momentum without energy?
Solution:
(i) Yes. A body at rest can have potential energy.
(ii) No. If momentum exists → motion exists → kinetic energy exists.
22. A boy weighing 40 kg and a girl weighing 30 kg climb 30 steps (each 20 cm) in 4 min and 3 min. Compare:
(i) Work done
(ii) Power developed
Solution:
Height = 30 × 0.2 = 6 m
(i)
Work done ∝ mgh
Ratio = 40 : 30 = 4 : 3
(ii)
Power ∝ Work / Time
Boy:Girl = 4/4 : 3/3 = 1 : 1
23. Differentiate between Potential Energy and Kinetic Energy
|
Potential Energy |
Kinetic Energy |
|
Energy due to position |
Energy due to motion |
|
= work done in lifting the body |
= work done before stopping a moving body |
|
Present even if body not moving |
Increases with speed |
24. Write transformation of energy in:
(i) Solar cell – Light → Electrical
(ii) Electric iron – Electrical → Heat
(iii) Induction cooker – Electrical → Heat
25. Passage-Based Question
(i) Work done is:
(A) Scalar
(B) Vector
(C) Tensor
(D) None
Ans. (A)
(ii) When force acts opposite displacement, work is:
(A) Positive
(B) Negative
(C) Both possible
(D) None
Ans. (B)
(iii) Define 1 J of work.
Ans: 1 J work is done when 1 N force displaces a body by 1 m in the direction of force.
26. Passage-Based Question on Potential Energy
(i) A body of mass 5 kg falls from 10 m to 4 m.
Find:
(a) Loss in PE
(b) Total energy at any instant
(g = 10 m/s²)
Solution:
At 10 m:
PE=mgh=5×10×10=500J
PE=mgh=5×10×10=500J
At 4 m:
PE=5×10×4=200J
PE=5×10×4=200J
Loss in PE = 500 – 200 = 300 J
Total mechanical energy = 500 J
(ii) Energy due to position is called:
(A) Potential energy
(B) Kinetic energy
(C) Nuclear energy
(D) None
Ans. (A)
27. Passage-Based Question on Conservation of Energy
(i) In an electric iron:
(A) Electrical → Heat
(B) Electrical → Light
(C) Heat → Electrical
(D) None
Ans. (A)
(ii) State law of conservation of energy.
Ans: Energy can neither be created nor destroyed; it only transforms from one form to another. Total energy remains constant.
(iii) In hydroelectric plant:
Ans: Potential energy of water → Electrical energy.
Benefits of Important Questions Class 9 Science Chapter 10
Enhanced Understanding : Answering important questions helps solidify your understanding of key concepts such as gravitational force, laws of gravitation and the motion of celestial bodies.
Preparation for Exams : Focusing on important questions allows you to identify the most critical topics and concepts that are frequently tested thereby improving your chances of performing well in exams.
Application of Concepts : These questions often require you to apply theoretical concepts to solve problems, which helps in better retention and understanding of the subject matter.
Time Management : Working through important questions can help you practice time management skills, as you learn to answer questions within a set timeframe similar to exam conditions.
Confidence Building : Successfully answering important questions boosts your confidence and prepares you mentally for the actual examination.
Comprehensive Coverage : They cover a wide range of topics within the chapter, ensuring that you are well-prepared for all aspects of the content.
Foundation for Advanced Topics : Understanding the fundamentals of gravitation in Class 9 sets a strong foundation for more advanced topics in higher classes, especially in physics.
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