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CBSE Notes
Class 9
Science
Chapter 10 Work and Energy

CBSE Class 9 Science Notes Chapter 10 Work and Energy

Work is a fundamental concept in physics that describes the transfer of energy when a force acts upon an object and causes it to move. It is a measure of how much energy is transferred by the force. Energy is the capacity to do work or produce change.

1.0Download Class 9 Science Notes Chapter 10 Work and Energy: Free PDF

Students can now download the CBSE Class 9 Science Chapter 10 Work and Energy notes for free in a well-organized PDF format. These notes are designed to help students grasp fundamental concepts in Physics, such as work, energy, power, and the different forms of energy, including kinetic and potential energy.

Class 9 Science Chapter 10 Revision Notes:

2.0Concept of Work

  • Work is done on an object when a force causes a displacement of the object.

Conditions that must satisfied for work to be done:

  1. A force should act on an object.
  2. The object must be displaced.
  3. The direction of Force must not be perpendicular to the displacement

Mathematical Definition of Work

  1. A constant force is applied in the direction of the displacement of an object.

Work = Force ✕ displacement

W = F ✕ s

Force and displacement is same direction

  1. A Constant force is applied at a certain angle with the direction of the displacement of an object.

Force and displacement at an angle

W = Fs Cos θ

  • Work is a scalar quantity.
  • SI Unit of work is Joule.
  • CGS Unit is Erg

Some important Points related to work

  1. If θ = 0° then Cos 0° = 1 and W = F ✕ s
  2. If θ = 90° then W = 0
  3. If θ = 180° then Cos 180° = -1 then W = -F ✕ s

Concepts of Positive and Negative Work

  • When angle between the force and displacement is acute i.e. 0°< θ < 90° The work done is positive.
  • When angle between the force and displacement is obtuse i.e. 90°< θ < 180° The work done is negative.
  • Whenever force is in the direction of motion, velocity of the object increases and work done is positive.
  • Whenever force opposes motion, velocity of object decreases and the work done is negative.
  • Work is positive when force and displacement are parallel to each other and that are in the same direction and work is negative when force and displacement are antiparallel to each other.

Condition for Zero Work

Condition for Zero work

Calculation of Work Done

The net force should be equal to zero

W = Fs Cosθ = 0 ✕ s ✕ Cosθ = 0

The net displacement should be equal to zero

W = Fs Cosθ = F ✕ 0 ✕ Cosθ = 0

The force and displacement should be perpendicular to each other

W = Fs Cosθ = F ✕ s ✕ Cos 90° = 0

3.0Energy

  • Energy is the capacity to do work, its unit is the same as that of work that is Joule(J).
  • IJ is the energy required to do 1 Joule of work. Sometimes a larger unit of energy called KiloJoule(kJ) is used. IKJ = 1000J

4.0Forms of Energy

The world around us offers energy in various forms, including potential energy, kinetic energy, thermal energy, chemical energy, electrical energy, and light energy.

  1. Mechanical Energy-The capacity to do mechanical work is called mechanical energy. Mechanical energy is of two types:

(a) Kinetic energy       

(b) Potential energy

Mechanical Energy = Kinetic Energy + Potential Energy

Also Read: Work, Energy and Power

5.0Key Features of Class 9 Science Notes Chapter 10 Work and Energy

  • Complete Coverage: Includes all key topics such as work, energy, power, types of energy, law of conservation of energy, and numerical problems related to work and energy.
  • Clear and Concise Explanations: Concepts are explained in simple and easy-to-understand language, making it easier for students to grasp complex topics.
  • Aligned with CBSE Curriculum: These notes are strictly in accordance with the latest CBSE syllabus and the NCERT textbook, ensuring all essential concepts are covered.
  • Formulae and Definitions: Essential formulas, definitions, and units related to work, energy, and power are clearly highlighted for quick reference.

Chapter-wise CBSE Notes for Class 9 Science:

Class 9 Science Chapter 1 - Matter in Our Surroundings Notes

Class 9 Science Chapter 2 - Is Matter Around Us Pure? Notes

Class 9 Science Chapter 3 - Atoms and Molecules Notes

Class 9 Science Chapter 4 - Structure of the Atom Notes

Class 9 Science Chapter 5 - Fundamental Unit of Life Notes

Class 9 Science Chapter 6 - Tissues Notes

Class 9 Science Chapter 7 - Motion Notes

Class 9 Science Chapter 8 - Force and Laws of Motion Notes

Class 9 Science Chapter 9 - Gravitation Notes

Class 9 Science Chapter 10 - Work and Energy Notes

Class 9 Science Chapter 11 - Sound Notes

Class 9 Science Chapter 12 - Improvement In Food Resources Notes


Chapter-wise NCERT Solutions for Class 9 Science:

Chapter 1: Matter In Our Surroundings

Chapter 2: Is Matter Around Us Pure?

Chapter 3: Atoms and Molecules

Chapter 4: Structure of the Atom

Chapter 5: Fundamental Unit of Life

Chapter 6: Tissues

Chapter 7: Motion

Chapter 8: Force and Laws of Motion

Chapter 9: Gravitation

Chapter 10: Work and Energy

Chapter 11: Sound

Chapter 12: Improvement in Food Resources

Frequently Asked Questions

Work is done when a force acts on an object and displacement occurs in the direction of force.

One joule is the amount of work done when a force of 1 N moves a particle 1 m in the direction of the force.

Chemical Energy of a battery is changed into heat energy and light energy.

Because when many balanced forces act on the object its displacement becomes zero.

A freely falling object eventually comes to a stop upon hitting the ground because its kinetic energy is transferred to the ground upon impact.

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