Work and Energy Class 9th Notes - Free NCERT Class 9 Science Chapter 11 Notes - Download PDF

CBSE Class 9 Work and Energy Notes - Download Free PDF

Welcome to our complete collection of Class 9 Science notes, which focuses on Chapter 11: Work, Power, and Energy. This meticulously crafted work and energy class 9 notes condenses the key concepts, important points, and essential diagrams from CBSE's Class 9 Science textbook, specifically Chapter 11. This chapter is critical for students using the NCERT Textbook to navigate the complexities of science. It teaches fundamental principles about work, power, and energy. Whether you need a quick review before an exam or want to gain a better understanding of the subject, these class 9 physics chapter 11 notes will help you along your academic journey.

Our CBSE class 9 physics ch 11 notes offer a structured approach to learning, with CBSE Key Notes, Revision Notes, Short Key Notes, and illustrative images and diagrams. We hope to make it easier to memorise and comprehend the subject matter by consolidating all relevant information in one place.

Furthermore, to supplement your understanding, we recommend that you read NCERT Solutions for Class 9 Science Chapter 11: Work, Power, and Energy to ensure a thorough understanding of the concepts covered. Download our PDF of work and energy notes class 9 for an easy revision experience, and start your journey to mastering this fundamental aspect of science education.

Also, students can refer,

• NCERT notes Class 9 Science
• NCERT solutions for class 9 science chapter 11 work and energy
• NCERT Exemplar Class 9 Science Solutions chapter 11 work and Energy
  

NCERT Class 9 Chapter 11 Notes

Work

Not much ‘work’ despite working hard

Performing physical or mental jobs is not considered work concerning this chapter.

The scientific concept of work-

Work is done on an object when it is displaced by the action of a force.

Work done by a constant force

Work done = force x displacement

W= Fs {F=force acting on the object, s= displacement caused due to F, W= work done on the object}

Work done by a constant force can be given by the multiplication of the magnitude of the force and the distance moved in the direction of that force. The SI unit of work done is ‘Nm’ (Newton metre) or ‘J’ (joule). When 1 N of force is applied to displace an object by 1m, 1 J of work is said to be done.

Work done could be either positive (force applied is in the direction of displacement) or negative (force applied is opposite to the direction of object’s displacement).

Energy

The Sun is the ultimate source of energy for sustaining life on Earth. Energy is defined as the capacity to do work. The object which performs work will lose energy, whereas the object on which work is being performed will gain energy. Transfer of energy happens when an object having energy starts to exert force on the other object. Energy has the same SI unit as of work i.e., joule (J), this is because energy is measured as the capacity to perform work. 1J work requires an input of 1J energy.

1 kJ= 1000J

Forms of energy

Energy can exist in the form of mechanical energy (potential energy + kinetic energy), heat energy, sound energy, chemical energy, and light energy and these forms of energy are interconvertible.

Kinetic energy

It is the energy possessed by an object due to its motion, it is directly proportional to the mass of an object and is proportional to the square of the object’s velocity.

Let there be an object of mass ‘m’, travelling with initial velocity ’u’. If a force ‘F’ acts on it to cause a displacement ‘s’, then its final velocity changes to ‘v’, and work done in it is ‘W’

W= Fs

From the equation of motion if a is the constant acceleration on a body;

v²-u²=2as

Rearranging the above equation gives

s=(v²-u²)/2a

Since, F=ma, work done can be written as,

W= ma x (v²-u²)/2a

Simplifying the above equation,

W= m(v²-u²)/2

If the object starts at rest, its initial velocity (u) =0

W= mv²/2

Since all work done on the object results in an increase in its kinetic energy,

Kinetic energy= E_k = mv²/2

where E_k= Kinetic energy of the object

m = mass of the object

v= velocity at which the object is moving

Potential energy

Potential energy can be defined as the energy possessed by an object by the virtue of its position or configuration.

The potential energy of an object at a height

When an object is raised to a greater height, its energy increases. This is because work is done on it as it is being raised against gravity. The gravitational potential energy is the energy present in such an item. The work done in elevating an object from the ground to a point above the ground is defined as the gravitational potential energy of that object.

Displacement of the object is its change in elevation=h, the force required for this action is mg, where m is the mass of that object is g is the acceleration due to gravity.

W= Force x displacement

W= mg x h

W= mgh

Since all work done on the object results in an increase in its potential energy,

Potential energy = E_P = mgh

Law of conservation of energy

It is only possible to transform energy from one form to another; it cannot be created or destroyed. Before and after the transition, the total energy of the system is the same. When an object of mass ‘m’ falls from height ‘h’ to the ground (h=0), its potential energy E_P = mgh gets converted to kinetic energy E_K = mv²/2, no energy is lost in this process.

mgh + mv²/2 = constant, mechanical energy is constant

Rate of doing work

Power is defined as the rate of doing work or the rate of transfer of energy.

Power = work/time

P=w/t

SI unit of power is Watt (W)

1W= 1 Js^-1

Average power is the total work divided by the total consumed time to perform that work.

Commercial unit of energy

Since a joule is very small, a larger unit kilowatt-hour (kW h) is used in commercial applications.

1 kW h is defined as the energy that is utilized in one hour at the rate of 1000 Js^-1 (or 1 kW).

1 kW h = 3.6 x 10⁶ J

1 unit of electricity consumed equals 1 kWh

Significance of NCERT notes for class 9 Science chapter 11

Comprehensive Revision: The NCERT work and energy class 9 notes provide a thorough overview of the chapter, assisting students with their revision efforts.

Clarity in Concepts: These class 9 physics chapter 11 notes are intended to simplify complex concepts so that students understand the main ideas and principles discussed in the chapter.

Step-by-Step Explanation: The work and energy notes class 9 provide a step-by-step explanation of various topics, allowing students to follow along and comprehend the material.

Aligned with CBSE Syllabus: As part of the CBSE Science syllabus for class 9, these notes have been meticulously crafted to cover all of the important topics and concepts outlined in the curriculum.

Non-Complex: The language used in these cbse class 9 physics ch 11 notes is straightforward and easy to understand, removing any confusion and assisting students in developing a solid foundation in the subject.

Offline Preparation: Students can download the notes in PDF format and access them offline, making it possible to prepare whenever and wherever they want.

NCERT solutions of class 9 subject-wise

• NCERT solutions for class 9 Maths
• NCERT solutions for class 9 Science

NCERT Class 9 Exemplar Solutions for Other Subjects:

• NCERT Exemplar Class 9 Maths solutions
• NCERT Exemplar Class 9 Science solutions

Class 10 Chapter Wise Notes