Question 1

Question 4Certain force acting on a 20 kg mass changes its velocity from 5 ms-1 to 2 ms-1. Calculate the work done by the force.

Accepted Answer

Given,Initial velocity u = 5 ms-1Mass of the body = 20 kgFinal velocity v = 2 ms-1Initial kinetic energyEi = 12\dfrac{1}{2}21​mu2Substituting we get,Ei = 12\dfrac{1}{2}21​ x 20 x 52= 10 × 25= 250 JFinal kinetic energyEf = 12\dfrac{1}{2}21​mv2= 12\dfrac{1}{2}21​ x 20 x 22= 10 × 4= 40 JAs, Work done = Change in kinetic energy = Ef – EiWork done = 40 J - 250 JWork done = -210 JHence, work done by the force = -210 J.

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 2

Question 5A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force? Explain your answer.

Accepted Answer

Given,Mass (m) = 10 kgWork done by gravity depends on the vertical displacement of the body. It is independent of the horizontal path.So, work done by gravity is = m g hWhere,Vertical displacement, h = 0 [∵ the line joining A and B is horizontal. ]∴ W = m × g × 0 = 0Hence, work done on object by gravity is zero.

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    .quick-rev ul { margin: 0; padding-left: 20px; }
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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 3

Question 6The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy? Why?

Accepted Answer

No. When the body falls from a height, its potential energy changes into kinetic energy progressively. A decrease in the potential energy is equal to an increase in the kinetic energy of the body. Hence, throughout the process, the total mechanical energy of the body remains conserved.Hence, the law of conservation of energy is not violated.

Web Content: Work and Energy | Bright Tutorials

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    .quick-rev ul { margin: 0; padding-left: 20px; }
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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 4

Question 7What are the various energy transformations that occur when you are riding a bicycle?

Accepted Answer

The rider's muscular energy is converted to heat energy and the bicycle's kinetic energy while riding a bicycle. Hence, energy transformations are :Muscular energy ⟶ Kinetic energy + Heat energy

Web Content: Work and Energy | Bright Tutorials

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 5

Question 8Does the transfer of energy take place when you push a huge rock with all your might and fail to move it? Where is the energy you spend going?

Accepted Answer

When we push a huge rock and fail to move it, our muscular energy is not transferred to the rock as kinetic energy as there is no displacement of the rock. However, as per the law of conservation of energy, our muscular energy is transformed into heat energy that heats up our body and makes us sweat.

Web Content: Work and Energy | Bright Tutorials

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    .quick-rev ul { margin: 0; padding-left: 20px; }
    .quick-rev li { margin-bottom: 6px; font-size: 0.92rem; }
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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 6

Question 9A certain household has consumed 250 units of energy during a month. How much energy is this in joules?

Accepted Answer

Given,Energy (E) = 250 units1 kWh = 3.6 x 106 J1 unit of energy = 1 kWhSo, 250 units of energy = 250 × 3.6 × 106 = 9 × 108 J.Hence, 250 units of energy = 9 × 108 J.

Web Content: Work and Energy | Bright Tutorials

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 7

Question 10An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.

Accepted Answer

Given,Mass (m) = 40 kgAcceleration due to gravity = 10 ms-2Height (h) = 5 mPotential energy = ?We know,Potential energy = m g hSubstituting we get,P.E. = 40 × 10 × 5 = 2000 JHeight when halfway down : = 52\dfrac{5}{2}25​ = 2.5 mPotential energy when halfway = ?Substituting we get,P.E. = 40 × 10 × 2.5 = 1000 JAccording to the law of conservation of energy:Total potential energy = potential energy halfway down + kinetic energy halfway down2000 = 1000 + K.E. halfway downK.E. at halfway down = 2000 - 1000 = 1000 JHence, Potential energy = 2000 J and kinetic energy at halfway down = 1000 joules.

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 8

Question 11What is the work done by the force of gravity on a satellite moving round the earth? Justify your answer.

Accepted Answer

When a satellite revolves around the earth in a circular orbit the work done is zero as force of gravity acting on satellite is perpendicular to its displacement.

Source: This question is from Work and Energy, Science &mdash; Class 9, CBSE Board.
Key Concepts CoveredThis question tests your understanding of the following concepts from the chapter Work and Energy: Question, Work, Done, Force, Gravity, Satellite. These are fundamental topics in Science that students are expected to master as part of the CBSE Class 9 curriculum.A thorough understanding of these concepts will help you answer similar questions confidently in your CBSE examinations. These topics are frequently tested in both objective and subjective sections of Science papers. We recommend revising the relevant section of your textbook alongside practising these solved examples to build a strong foundation.
How to Approach This QuestionRead the question carefully and identify what is being asked. Break down complex questions into smaller parts. Use the terminology and concepts discussed in this chapter. Structure your answer logically — begin with a definition or key statement, then provide supporting details. Review your answer to ensure it addresses all parts of the question completely.
Key Points to RememberRead the question carefully and identify all parts before answering.
Use the terminology specific to this subject and chapter.
Review the textbook content for this chapter before attempting questions.
Practice writing concise, well-structured answers within time limits.
Related Questions from Work and EnergyQ1: Question 1 What is power?
Q10: Question 10 An object of mass 40 kg is raised to a height of 5 m above the ground. What is its...
Q12: Question 12 Can there be displacement of an object in the absence of any force acting on it? Think....
Q13: Question 13 A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done...
Q14: Question 14 An electric heater is rated 1500 W. How much energy does it use in 10 hours?
Practice more questions from Work and Energy &mdash; Science, Class 9 CBSE

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    .quick-rev li { margin-bottom: 6px; font-size: 0.92rem; }
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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 9

Question 12Can there be displacement of an object in the absence of any force acting on it? Think. Discuss this question with your friends and teacher

Accepted Answer

Yes, a uniformly moving object can experience displacement even when no force is acting on it. According to Newton's first law of motion, an object in motion will continue in its straight-line motion unless acted upon by an external force. Therefore, displacement of an object can occur in the absence of any force acting on it.

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    .quick-rev h3 { color: var(--bt-primary); margin-top: 0; }
    .quick-rev ul { margin: 0; padding-left: 20px; }
    .quick-rev li { margin-bottom: 6px; font-size: 0.92rem; }
    .keyword-tags { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0; }
    .keyword-tags span { background: var(--bt-primary-light); color: var(--bt-primary-dark); padding: 3px 10px; border-radius: 12px; font-size: 0.78rem; font-weight: 600; }

BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 10

Question 13A person holds a bundle of hay over his head for 30 minutes and gets tired. Has he done some work or not? Justify your answer.

Accepted Answer

Work is said to be done when force applied on an object shows the displacement in that object. In this case, as there is no displacement of the hay bundle, hence no work is done.

Source: This question is from Work and Energy, Science &mdash; Class 9, CBSE Board.
Key Concepts CoveredThis question tests your understanding of the following concepts from the chapter Work and Energy: Question, Person, Holds, Bundle, Hay, Head. These are fundamental topics in Science that students are expected to master as part of the CBSE Class 9 curriculum.A thorough understanding of these concepts will help you answer similar questions confidently in your CBSE examinations. These topics are frequently tested in both objective and subjective sections of Science papers. We recommend revising the relevant section of your textbook alongside practising these solved examples to build a strong foundation.
How to Approach This QuestionRead the question carefully and identify what is being asked. Break down complex questions into smaller parts. Use the terminology and concepts discussed in this chapter. Structure your answer logically — begin with a definition or key statement, then provide supporting details. Review your answer to ensure it addresses all parts of the question completely.
Key Points to RememberRead the question carefully and identify all parts before answering.
Use the terminology specific to this subject and chapter.
Review the textbook content for this chapter before attempting questions.
Practice writing concise, well-structured answers within time limits.
Related Questions from Work and EnergyQ1: Question 1 What is power?
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Q12: Question 12 Can there be displacement of an object in the absence of any force acting on it? Think....
Q14: Question 14 An electric heater is rated 1500 W. How much energy does it use in 10 hours?
Q15: Question 15 Illustrate the law of conservation of energy by discussing the energy changes which...
Practice more questions from Work and Energy &mdash; Science, Class 9 CBSE

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 11

Question 14An electric heater is rated 1500 W. How much energy does it use in 10 hours?

Accepted Answer

Given,Power of the heater = 1500 WConverting W to kW1000 W = 1 kWSo, 1500 W = 15001000\dfrac{1500}{1000}10001500​ = 1.5 kWTime taken = 10 hWe know,Power = Energy consumedTime taken\dfrac{	ext{Energy consumed}}{	ext{Time taken}}Time takenEnergy consumed​OrEnergy consumed = Power x Time takenSubstituting we get,Energy consumed = 1.5 x 10 = 15 kWhConverting kWh to J1 kWh = 3.6 x 106 JSo, 15 kWh = 3.6 x 106 x 15 = 5.4 x 107 JHence, the energy consumed = 5.4 x 107 J

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 12

Question 15Illustrate the law of conservation of energy by discussing the energy changes which occur when we draw a pendulum bob to one side and allow it to oscillate. Why does the bob eventually come to rest? What happens to its energy eventually? Is it a violation of the law of conservation of energy?

Accepted Answer

The law of conservation of energy states that energy can only be converted from one form to another; it can neither be created or destroyed. The total energy before and after the transformation remains the same.Refer the figure of an oscillating pendulum bob shown below:The kinetic energy decreases and the potential energy becomes maximum at B.After a moment the the to and fro movement starts again.So, from B to A, again the potential energy changes into kinetic energy and this process repeats again and again.So, when the bob is in its state of to and fro movement it has potential energy at the extreme position B or C and kinetic energy at resting position A.It has both the kinetic energy and potential energy at an intermediate position. However, the sum of kinetic and potential energy remain same at every point of movement.The bob will eventually come to rest due to the frictional resistance offered by air on the surface of bob and pendulum loses its kinetic energy to overcome this friction and finally comes to rest.The law of conservation of energy is not violated because the kinetic energy lost by the pendulum to overcome the friction is gained by surroundings. Hence, total energy of the system will remain conserved.

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 13

Question 16An object of mass, m is moving with a constant velocity, v. How much work should be done on the object in order to bring the object to rest?

Accepted Answer

The kinetic energy of an object of mass m, moving with a velocity, v, is given by the expression,Kinetic energy = 12\dfrac{1}{2}21​mv2In order to bring it to rest, its velocity has to be reduced to zero.An external force has to absorb energy from the object, i.e., do negative work on it, equal to its kinetic energy = −12-\dfrac{1}{2}−21​mv2

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 14

Question 17Calculate the work required to be done to stop a car of 1500 kg moving at a velocity of 60 kmh-1.

Accepted Answer

Given,Mass (m) = 1500 kgInitial velocity (v) = 60 kmh-1Final velocity = 0Converting kmh-1 to ms-1 : multiply by 518\dfrac{5}{18}185​60 x 518\dfrac{5}{18}185​ = 503\dfrac{50}{3}350​ ms-1Work required to stop the moving car = Kinetic energy of car (K.E.)K.E. = 12\dfrac{1}{2}21​mv2= 12\dfrac{1}{2}21​ x 1500 x (503)(\dfrac{50}{3})(350​)2= 12\dfrac{1}{2}21​ x 1500 x 25009\dfrac{2500}{9}92500​= 208333.3 JHence, work done = 208333.3 J.

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 15

Question 18In each of the following a force, F is acting on an object of mass, m. The direction of displacement is from west to east shown by the longer arrow. Observe the diagrams carefully and state whether the work done by the force is negative, positive or zero.

Accepted Answer

Case IThe direction of force acting on the block is perpendicular to the displacement. Hence, work done by force on the block will be zero.Case IIThe direction of force acting on the block is in the direction of displacement. Hence, work done by force on the block will be positive.Case IIIThe direction of force acting on the block is opposite to the direction of displacement. Hence, work done by force on the block will be negative.

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 16

Question 19Soni says that the acceleration in an object could be zero even when several forces are acting on it. Do you agree with her? Why?

Accepted Answer

Acceleration in an object could be zero even when several forces are acting on it. This happens when all the forces cancel out each other i.e., the net force acting on the object is zero.Consider the below object:F = maF = 0 [∵ equal and opposite forces cancel out each other]∴ 0 = ma⇒ a = 0∴ Vfinal = VinitialHence, if the object was initially moving, it will continue to move with uniform velocity without acceleration.Therefore, I agree with Soni's statement.

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 17

Question 20Find the energy in joules consumed in 10 hours by four devices of power 500 W each.

Accepted Answer

Given,Power rating (P) = 500 WConverting W into kW1000 W = 1 kW500 W = 5001000\dfrac{500}{1000}1000500​ = 0.5 kWTime (T) = 10 hWe know,Power = Energy consumedTime taken\dfrac{	ext{Energy consumed}}{	ext{Time taken}}Time takenEnergy consumed​OrEnergy consumed by each device = Power x Time takenSubstituting we get,Energy consumed by each device = 0.5 x 10 = 5 kWhEnergy consumed by four devices = 4 x 5 = 20 kWhConverting kWh to J1 kWh = 3.6 x 106 JSo, 20 kWh = 3.6 x 106 x 20 = 7.2 x 107 JHence, the energy consumed = 7.2 x 107 J

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 18

Question 21A freely falling object eventually stops on reaching the ground. What happens to its kinetic energy?

Accepted Answer

When an object falls freely towards the ground, its potential energy decreases, and kinetic energy increases. As the object touches the ground, all its potential energy becomes kinetic energy. When the object hits the ground, all its kinetic energy gets converted into heat energy and sound energy.

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 19

Question 2Write an expression for the kinetic energy of an object.

Accepted Answer

Kinetic Energy (KE) = 12\dfrac{1}{2}21​mv2. Its SI unit is Joule (J).

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Question 20

Question 3The kinetic energy of an object of mass m, moving with a velocity of 5 ms-1 is 25 J. What will be its kinetic energy when its velocity is doubled? What will be its kinetic energy when its velocity is increased three times?

Accepted Answer

Given,Kinetic Energy (KE) = 25 JVelocity (v) = 5 ms-1We know,Kinetic Energy (KE) = 12\dfrac{1}{2}21​mv2.Substituting we get,25 = 12\dfrac{1}{2}21​ x m x 5225 x 2 = 25 x mm = 5025\dfrac{50}{25}2550​m = 2 kgWhen velocity is doubled :v' = 10 ms-1m = 2 kgSubstituting we get,KE = 12\dfrac{1}{2}21​ x 2 x 102K.E. = 100 JWhen velocity is increased three times, thenv'' = 15 ms-1m = 2 kgSubstituting we get,KE = 12\dfrac{1}{2}21​ x 2 x 152K.E. = 225 JHence, Kinetic Energy becomes 100 J when velocity is doubled and it becomes 225 J when velocity is increased three times.

Web Content: Work and Energy | Bright Tutorials

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BRIGHT TUTORIALS
  BRIGHT TUTORIALSCBSE Class IX | Academic Year 2026-20279403781999Excellence in Education
  Science | Chapter 10: Work and EnergyWeb Content &mdash; Quick Reference
  
    Chapter 10: Work and Energy &mdash; Quick Reference

work
      kinetic energy
      potential energy
      conservation of energy
      power
      kWh

Quick Revision Points
      
        Work W = Fs cosθ (joule); W = 0 when F ⊥ s or displacement = 0
KE = ½mv²; PE = mgh; Work-energy theorem: W = ΔKE
Conservation: energy transforms but total remains constant; PE + KE = constant in free fall
Power P = W/t (watt = J/s); 1 HP = 746 W
1 kWh = 3.6 × 10⁶ J = 1 unit of electricity

Exam Tips for Chapter 10
      
        Read the detailed chapter notes for complete coverage of all NCERT topics.
        Practice all NCERT in-text and back exercise questions &mdash; they are frequently asked in exams.
        Focus on comparison tables, diagrams, and definitions &mdash; these are high-scoring areas.
        For numericals (if applicable), practice at least 20 problems of varying difficulty.
        Refer to the practice question bank (200+ questions) for thorough preparation.

Related Resources
      
        Detailed Notes: ch10-work-and-energy.html
        Practice Questions: 100+ questions with answers in 05-practice-questions/
        Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
        Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html

BRIGHT TUTORIALSContact: 9403781999 | CBSE Class IX Coaching | 2026-2027

Work and Energy

Exercises

Intext Questions 3

Intext Questions 5