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

The chapter work, energy and power is the continuation of the NCERT chapter System of particles and Rotational motion. The ncert Class 11 Physics chapter 6 notes covers a brief outline of the chapter work, energy and power. The main topics covered in work, energy and power Class 11 notes introduction to the concept of work done by a body, work and kinetic energy concepts include the work-energy theorem, work, and kinetic energy.

Work is carried out by a variable force, potential energy, spring’s potential energy, the rule of conservation energy, power, and collisions are all examples of different types of energy. The basic equations in the chapter are also covered in the Class 11 Physics chapter 6 notes. The relevant derivations are not addressed in the CBSE physics chapter 6 notes for Class 11 students.

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

Work, Energy, and Power Class 11 Notes Physics Chapter 6

Work is said to be done once a force applied on the body displaces the body through a particular distance within the direction of applied force.

• The definition of Work in CBSE Class 11 Physics chapter 6 notes is the work w done by the agent is the product of the element of force in the direction of movement (displacement) and the magnitude of displacement.

Word done is scalar quantity, valued or measured in newton meter.

The dimension of work is ML²T²

Significant about work done, derived from the definition given above.

1. Work is done by force is 0 if the movement or displacement is perpendicular to the force (θ=90^o).

2. Work done by the force is positive if angle betwixt force and movement is acute (θ<90^o).

3. Work done by the force is negative if angle betwixt force and movement is obtuse((θ>90^o).

4. If the pertained force differ with time/position, the work done is given by:

5. If a spring is stretched or compressed by a small interval from its unstretched configuration, the spring will pull a force on the block given byF=-kx, where x compression in spring is, k is a constant which is called a spring constant

6. The negative sign represents that the direction of the spring force is averse tox, the displacement of the free-end.

Work done by spring when block is moved by x₀ is shown by

Work done by an agent in giving an elongation of x₀ is represented as 0.5kx₀².

Now, from the Class 11 Work, Energy, and power notes, after work, we discuss energy. So let’s see.

Energy

The energy of a particle or an object or a body is its capacity or efficiency to do work. Anything which is liable to do work is said to obtain energy.

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

There are 2 kinds of mechanical energy one is kinetic energy and other is potential energy.

• Kinetic Energy

The energy obtained by a body or an object by attribute of its motion is known as its kinetic energy.

For an object or a body of mass m and having a velocity v, the kinetic energy is given by:

• Potential Energy

The energy obtained by a body or an object by attribute of its position is known as its potential energy.

There are 2 common types of potential energy, one is gravitational and other is elastic.

• Gravitational potential energy of a particle or a body or an object is the energy obtained by the body by virtue of its position above the surface of the earth.

It is represented by

Where the mass of a body is m, g is indicate for acceleration due to gravity on the earth surface, and the height by which the body is lifted is h. Work must be done in opposition to the restoring elastic force when an elastic body is displaced from its equilibrium state. The object or particle stores the work done in the form of elastic potential energy.

If an elastic spring is compressed (or strained) by a distance Y from its equilibrium state, then its elastic potential energy is represented by

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

Work-Energy Theorem

The work done by a force on a body or an object, in pursuance to the work-energy theorem, is equal to the change in kinetic energy of the object.

w= Change in K. E. of a body =Δ KE

Δ KE - The difference between the final and initial kinetic energies of the body.

Energy and momentum are related by , E=p²/2m, where m is the mass.

• The Law of Conservation of Energy

The total energy of a separated system does not vary according to the rule of conservation of energy. Although energy can be transmuted from one form to another, the overall energy of a separated or isolated system does not change.

• Energy can neither be created, nor destroyed.

Apart from mechanical energy, the energy may declare itself in many other forms. Few of these forms are: electrical energy, thermal energy, chemical energy, visual light energy, nuclear energy etc.

• Equivalence of Mass and Energy

In accordance with Einstein, mass and energy are interconvertible. That is, mass can be modified into energy and energy can be modified into mass.

The energy E is equivalent to mass m is represented by relation

E=mc², where c=3*10⁸m/s, velocity of light in vacuum or air.

When an object displace with a velocity v, comparable to the velocity of light 'c' its mass m is represented by

where m₀ its rest mass. Now, after work and energy, we discuss Power.

Power

Power is the scalar quantity.

It is the speed or rate of doing work; it means the work done per unit time.

Where, α= angle between the force F and the velocity v.

The SI unit of power is watt, i.e. 1watt=1Js^-1.

The dimensional unit of power is ML²T^-3.

The other units that are used for power are

1Kilowatt =1kW=10³W

1 megawatt =1MW=10⁶W

horse power .746kW.

Collision

Collision is defined as an isolated or separated event in which 2 or more colliding objects for a short period of time, bodies exert rather powerful forces on each other. A collision between particles or materials has been categorized into two categories.

1. Elastic collisions

2. Collisions that is inelastic.

If both the impulse momentum or linear momentum and the kinetic energy of the system are preserved, a collision between two objects or bodies is said to be elastic.

Collisions of atomic molecules, atoms, marble balls, and billiard balls are the examples.

Collision that is inelastic or inelastic collision

If the system’s impulse momentum remains constant, the collision is said to be inelastic.

When we pull a ball of wet putty down onto the floor, the contact between the ball and the floor is an example of inelastic.

• If the colliding molecules displace along the same straight line path both before and after the collision, the collision is said to be one dimensional.

• In a one dimensional elastic collision, the relative velocity of approach before collision is equal to the relative velocity of separation after collision.

If two objects of mass m1 and m2 displacing with velocities u₁ and u₂ resp. collide head on such that v₁ and v₂ be their respective velocities after collision, then,

Significance of NCERT Class 11 Physics Chapter 6 Notes

Class 11 notes on work, energy, and power will help you review the chapter and obtain a better understanding of the important themes addressed. This NCERT Class 11 Physics chapter 6 notes are also beneficial for competitive exams such as VITEEE, BITSAT, JEE Main, NEET, and others, as they cover the main themes of the CBSE Physics syllabus. You can use the Class 11 Physics chapter 6 notes pdf download to study offline.

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