The Work, Energy, and Power Class 11 Physics Chapter 5 notes is one of the best resources to prepare for your physics for the Board exam. It includes the explanation of the fundamental concepts of Work, movement of an object and Energy in simple as well as precise form. This blog article highlights the types of Energy and the relation between the mass and energy of an object. This Class 11 Physics Chapter 5 notes can be an integral part of exam preparation as it helps in revising the important topics of this chapter quickly and effectively. The purpose of the notes is to make the complex concepts of physics easy to recall for the candidates of the Board exam.
Definition of Work
The work is done when a force is applied on an object to change its place by a certain distance in the direction of the applied force.
- Work is the product of the applied force in the direction of displacement and distance.
- Dimensional expression of work is ML2 T2
- SI unit of work is Joule (J)
- CGS unit of work is Erg
- 1 joule = 107 erg
- Work is a scalar quantity.
Types of work
Positive work
If the angle between F and s is acute, then the work is called Positive work.
Negative work
If the angle between F and s is obtuse it is called negative work.
Zero work
If the object moves perpendicular to the direction of the force, the work is zero. θ = 90°
Power
Power: The amount of work done per unit of time is called Power.
- p= W/t=FXs / t
- s/t= v; v = uniform velocity at which the object is moving
- P = Fx v = F v cos θ
- Dimensional expression of work is ML2 T-3
- Another unit of Power is horsepower
- 1 horsepower power= 746 watt
Energy
The capacity to do work can be defined as Energy.
Energy is a scalar unit
There are different types of energy, such as chemical energy, heat energy, electric energy, mechanical energy, sound energy, etc.
- The SI unit of energy is the Joule (J)
- CGS unit of Energy is Erg
Mechanical Energy
Law of Conservation- There are two types of mechanical energy, and those are Kinetic energy and Potential energy. The sum of potential energy and kinetic energy always remains constant during the motion. It does not vary depending on the time. This is called the Law of Conservation of Mechanical Energy.
Energy and Mass energy
According to the Einstein mass-energy equivalence principle, energy and mass can be changed into each other, which means they are in an interconvertible relation.
E=mc2
[Where m= mass, c= speed of light]
Kinetic energy
An object that gains energy due to its motion is called Kinetic energy.
k = 1 / 2 mv2 = p2 / 2m
[Here, m = mass;v= velocity and p= momentum of the object]
Potential Energy
The energy in an object due to its position is called Potential energy. Work, Energy, and Power Class 11 Physics Chapter 5 notes include the types of Potential energy.
- Gravitational Potential Energy- An object that possesses the energy produced by its position on the Earth’s surface is called the gravitational energy.
If an object is raised to a certain height against gravity and the mass of the object is expressed by m, then the gravitational energy will be mgh.
- Elastic Potential Energy – When an elastic body is stretched from its equilibrium position, the energy stored in it is known as Elastic Potential Energy.
The Elastic Potential Energy of a spring is U = 1.2 kx²
[Where U is Elastic Potential Energy, x is displacement from the equilibrium position, and k is the spring constant]
- Electric Potential Energy – A charged particle possesses the energy due to its position in the electric field, which is called Electric Potential Energy.
Work Energy Theorem
As per the work-energy theorem, the kinetic energy of an object is equal to the work done by applying a force on a body. According to this theory, the kinetic energy can not be gained or lost if a force acts on an object.
Conservative Force and Non-conservative Forces
The difference between the Conservative and Non-conservative forces is presented in the following table:
| Factors | Conservative force | Non-Conservative force |
| Path | Work done by this force depends on the starting and end points. | Work depends on the path that has been taken |
| Closed path | Work done in a closed path | Work done over a closed path is not zero. |
| Recoverability | Work done can be recovered | Work done is not recoverable |
| Energy | It conserves mechanical energy and can be associated with potential energy. | It can not conserve the mechanical energy |
| Example | Gravitational force, Elastic force | Air resistance, frictional force |
Motion in a vertical circle
- It is a non-uniform circular motion.
- When an object moves in a vertical plane with a certain speed, the force applied to it is constantly changed due to gravity.
- Because of gravity, the speed of the object is minimum at the highest point, and it becomes minimum at the lowest point.
- The speed remains constant, and the gravity does not directly affect the centripetal force.
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Conclusion
Work, Energy, and Power Class 11 Physics Chapter 5 notes focus on highlighting the key points of this important chapter. All the important details regarding the movement of an object and the Energy obtained by an object have been illustrated in simple language. The types of Potential energy and Mechanical Energy are presented by discussing their features. The basic difference between Conservative force and non-conservative force has been presented briefly for the ease of the students.
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