NCERT Class 11 Physics Chapter 6 Work, Energy and Power Notes - Download PDF

Did you know why certain phenomena occur, like the peculiar case where someone is stationary at a point while holding a mass on their head, yet no work is done? The concepts explaining such intriguing situations are precisely what we explore in this class 11 physics chapter 6 notes on Work, Energy, and Power.

These Work Energy and Power class 11 notes aren't just essential for acing board or state exams; they are crucial for competitive exams like JEE Main, NEET, and various state engineering exams such as WBJEE, BCECE, and more. Whether you aim for excellence in exams, class tests, assignments, or a deeper understanding of the subject, the role of these Work, Energy and Power notes class 11 cannot be overstated.

Recognizing their significance, the experts at Careers360 have meticulously crafted CBSE class 11 physics ch 6 notes, addressing the nuances of phenomena like the absence of work in a stationary scenario. The comprehensive nature of these ch 6 physics class 11 notes extends across all chapters, providing a valuable resource for free, available in PDF format. This flexibility allows students to choose between online and offline study options.

So, dive into these physics class 11 chapter 6 notes pdf to unravel the mysteries behind intriguing phenomena, and let them be your guide to success in both academics and competitive exams.

Also, students can refer,

• NCERT Solutions for Class 11 Physics Chapter 6 Work, Energy, and Power.
• NCERT Exemplar Class 11 Physics Chapter 6 Solutions Work, Energy and Power

Introduction

The terms 'work,' 'energy,' and 'power' appear in everyday conversations with different connotations. Consider a construction worker lifting heavy bricks or a student carrying a rucksack up a flight of stairs—both are examples of people putting in effort or doing work.

Now let's look at the concept of energy. Consider a tennis player serving a powerful shot. The player's ability to propel the ball from rest to rapid movement demonstrates the presence of energy. In this case, energy manifests as the ability to cause a change in the state of an object.

Moving on to power, imagine a sprinter accelerating quickly during a race. The sprinter's ability to cover a long distance in a short period of time demonstrates a high power output. In physics, power is precisely defined as the rate at which work is done or energy is transferred, with an emphasis on the speed at which these actions take place.

Work occurs when a force is applied to a body, causing it to move in the direction of the force.

Work Done by a Constant Force

If a constant force F is applied to a body at an angle θ with the horizontal, and the body is displaced through a distance ss, then the work done (Work) can be expressed using the formula:

Work (W) F.S. cosθ

• Dimension of work: [ML²T^-2]
• Unit: The units of work are of two types (i) Absolute units and (ii) Gravitational units

(i) Absolute units: Joule [S.I.] and Erg [C.G.S.]

(ii) Gravitational units: kg-m [S.I.] and gm-cm [C.G.S.]

Nature of Work Done

1. Positive work: Positive work occurs when the force applied to an object is parallel to the direction of displacement. This collaboration between force and displacement is quantified as positive work, which indicates that the external force supports and promotes the object's motion. Examples of positive work include lifting a body against gravity or stretching a spring.

• Maximum work(W_max): FS [When cosθ is maximum, i.e. θ=0^o]

2. Negative work: Negative work occurs when a force is applied in the opposite direction of the displacement. This opposition between force and displacement produces negative work, indicating that the external force slows or opposes the object's motion. When a person lowers a body to the ground against gravity, they are performing negative work.

• Minimum work(Wmin): -FS [When cosθ is -1, i.e. θ=180^o]

3. Zero work: under three specific conditions, the work done becomes zero as expressed by the equation: Work (W) F.S. cosθ

• If the force is perpendicular to the displacement.
• If there is no displacement, i.e. S=0
• If there is no force acting on the body, i.e. F=0

Work Done by a Variable Force

If the applied force (F) varies along the path, the work required to move a body from position A to B can be calculated by integrating the product of the force and differential displacement.

Work Done Calculation by Force Displacement Graph

The work done by a force on an object can be calculated using the area under the force-displacement graph.

Energy

The energy of a body is essentially its ability or capacity to get things done, or in other words, to do work.

• The SI unit of energy is the same as the work is Joule (J).

Kinetic Energy

Kinetic energy is the energy possessed by an object due to its motion.

Where: KE is the kinetic energy, m is the mass of the object and v is its velocity.

Relation of kinetic energy with linear momentum

Potential Energy

Potential energy is the energy that an object has because of its position or state.

Where, U is the potential energy, m is the mass of the object, g is the acceleration due to gravity and h is the height of the object above a reference point.

Types of Potential Energy

Gravitational Potential Energy (GPE): As described above, it's associated with an object's height in a gravitational field.

Elastic Potential Energy: For objects like springs or rubber bands, the potential energy is associated with how much the material is stretched or compressed.

When an elastic spring is compressed (or strained) by a distance x from its equilibrium state, its elastic potential energy is represented by:

Where, k is the force constant of a given spring.

Work-Energy Theorem

It states that the work done on an object is equal to the change in its kinetic energy. Mathematically, it is expressed as:

W= Change in K. E. of a body =Δ KE

Or,

Where, v_o is initial velocity and v is final velocity

Law of Conservation of Energy

The Law of Conservation of Energy asserts that energy is neither created nor destroyed; it merely changes from one form to another.

1. Conservation of Mechanical Energy: In systems where only conservative forces are at play, the total mechanical energy (sum of kinetic and potential energy) remains constant. This principle is expressed as K + U = E, where K is the kinetic energy, U is the potential energy, and E is the total mechanical energy. The conservation of mechanical energy implies that in the absence of non-conservative forces like friction or air resistance, the total energy within the system remains unchanged.
2. Law of Conservation of Total Energy: This law states that while energy may transform from one type to another, the total energy within an isolated system remains constant. In other words, energy cannot be created or destroyed; it can only change forms. This principle is a fundamental concept in physics and holds true for various physical processes.

Power

The power (P) of a body is defined as the rate at which the body can do work. Mathematically, power is expressed as the amount of work done (W) divided by the time (t) taken to do that work. The formula for power is:

• Dimension of power: [ML²T^-3]
• Unit of power: Watt or Joule/sec [S.I.], Erg/sec [C.G.S.]
• Practical unit: : Kilowatt (kW), Mega watt (MW) and Horse power (hp)

Collision

A collision occurs when two or more objects come into contact for a short period, during which they exert forces on each other. These forces can cause changes in the motion of the objects involved. Collisions are important because they help us understand how momentum and kinetic energy are transferred and conserved.

Types of collision

On the basis of conservation of kinetic energy, there are mainly three types of collision

• Perfectly Elastic Collision: In a perfectly elastic collision, the system's kinetic energy is conserved, which means that the total kinetic energy before and after the collision is the same. There is no net loss or gain in kinetic energy, and the objects involved bounce off each other without deforming or losing energy to other forms.
• Inelastic collision: In an inelastic collision, the system's kinetic energy is not conserved; that is, the kinetic energy after the collision differs from the kinetic energy before the collision. Some of the initial kinetic energy is converted into different forms, such as internal energy, heat, or deformation.
• Perfectly inelastic collision: Inelastic collisions occur when the kinetic energy after the collision is less than the kinetic energy before the collision. In inelastic collisions, some of the initial kinetic energy is converted into other forms, while the total kinetic energy is not conserved.

Types of collision based on the the direction of colliding bodies

• Head on or one dimensional collision: when the motion of colliding particles before and after the collision occurs along the same line, it is referred to as a "head-on" or "one-dimensional" collision. In such collisions, the initial and final velocities of the particles are aligned along a straight line, simplifying the analysis of the collision dynamics.

• Perfectly Elastic Oblique Collision:

Let two bodies move as shown in the figure. By the law of conservation of momentum,

• Perfectly Inelastic Collision

After a collision, two bodies stick together, resulting in a final common velocity.

• When the colliding bodies are moving in the same direction

• When the colliding bodies are moving in the opposite direction

How to Use Physics Class 11 Chapter 6 Notes PDF Effectively

Review regularly: Set up regular review sessions to reinforce your understanding of the concepts. Repetition is essential for retaining information.

Understand key concepts: Ensure that you understand fundamental concepts such as work, energy, and power. If there is any confusion, refer to your textbook or other resources for clarification.

Create concept maps: Concept maps or diagrams can help you visualise the relationships between different concepts. This can help you see the big picture and how different ideas connect.

Practice problem-solving: The most effective way to learn physics is to solve problems. Work through the example problems in your notes and try some extra exercises from your textbook or other resources.

Connect Theory and Applications: Apply theoretical concepts to real-world applications. Understand the principles discussed in the notes.

Join study groups: Join study groups to discuss concepts with your peers. Explaining ideas to others and hearing different perspectives can help you gain a better understanding.

Seek clarification: If you have any problems or questions, do not hesitate to seek clarification from your teacher, classmates, or online resources.

Key features of Units and Measurements class 11 notes

• These physics class 11 chapter 6 notes pdf are perfectly aligned with the CBSE Physics Syllabus for Class 11 and cover all essential topics and concepts.
• These CBSE class 11 physics ch 6 notes are written in clear and simple language to help students understand complex physics concepts easily.
• These Work Energy and Power Notes class 11 summarise key points, formulas, and principles throughout Chapter 6, providing comprehensive coverage. This unified view allows students to grasp the entire content.
• These notes help students quickly review key concepts before exams, improving their understanding and preparation.
• These class 11 physics chapter 6 notes, available for free in both physical and digital formats, allow for flexibility in study preferences while also ensuring easy access and sharing.
• These Work Energy and Power class 11 notes can also help prepare for competitive exams like JEE Main and NEET. They cover the core concepts of the CBSE Physics Syllabus, laying a strong foundation for competitive exams.

Significance of NCERT Class 11 Physics Chapter 6 Notes

Class 11 notes on work, energy, and power facilitate a thorough review of the chapter, enhancing comprehension of key concepts. These NCERT Class 11 Physics chapter 6 notes prove advantageous for competitive exams like VITEEE, BITSAT, JEE Main, NEET, covering essential topics from the CBSE Physics syllabus. The PDF download option allows convenient offline study.

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