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Ever wondered how things move, why they stop, or how much effort it takes to get them going? That is exactly what you will explore in NCERT Notes Class 11 Physics Chapter 6: Work, Energy and Power. This chapter is very important to understand how force leads to motion and how energy flows in different forms. It forms the foundation for many real world concepts and is vital for students preparing for CBSE board exams, JEE, and NEET. These NCERT Notes are prepared by our expert faculty based on the latest CBSE syllabus.
In these Work, Energy and Power Class 11 Notes PDF, you will find clear explanations of work done by a force, kinetic and potential energy, conservation of mechanical energy, and the concept of power. These NCERT Notes for class 11 also include important formulas, and diagrams. Whether you are preparing for exams or strengthening your basics, these NCERT notes will make your learning more structured and effective.
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There are two ways of multiplying vectors (i) scalar product (ii) vector product. We shall study the latter in next chapter. The scalar product or dot product of any two vectors
where
This concept explains how work done on an object results in a change in its kinetic energy. When a force causes displacement, work is said to be done. The Work-Energy Theorem states that the net work done by all forces on an object is equal to the change in its kinetic energy.
If a force
The work done by the force is defined as the product of component of the force in the direction of the displacement and the magnitude of this displacement.
So,
(i) Absolute units: Joule [S.I.] and Erg [C.G.S.]
(ii) Gravitational units: kg-m [S.I.] and gm-cm [C.G.S.]
Negative work :
Zero Work:
The work done by a force on an object can be calculated using the area under the force-displacement graph.
The energy of a body is essentially its ability or capacity to get things done, or in other words, to do work.
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.
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.
Relation of kinetic energy with linear momentum
Confining to one dimension, rate of change of kinetic energy with time is
[Integrating from the initial position
Where
or
Thus,
Thus, work-energy theorem is proved for a variable force.
Potential energy is the energy that an object has because of its position or state.
Types of Potential Energy
Gravitational Potential Energy (GPE): It is the energy associated with an object's height in a gravitational field.
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.
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.
The Law of Conservation of Energy asserts that energy is neither created nor destroyed; it merely changes from one form to another.
For simplicity, we are considering one-dimensional motion. Suppose that a body undergoes displacement
If the force is conservative, the potential energy function
Adding the above two equations, we get
or
Over the whole path
The quantity
When a spring is either compressed or stretched from its natural (equilibrium) position, it stores potential energy due to its elasticity. This energy is known as elastic potential energy.
According to Hooke's Law, the force required to stretch or compress a spring is:
where:
The potential energy stored in the spring is given by the formula:
This energy increases with greater displacement and depends on the stiffness of the spring (value of
The work done against which is stored in the system as its potential energy, which can be recovered later, is called a conservative force.
The work done against which is not stored in the system as its potential energy, which can be recovered later, is called non-conservative force".
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:
Average
Instantaneous
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.
On the basis of conservation of kinetic energy, there are mainly three types of collision
From equation (1) and (2) We get,
From equations (1),(2), (3) We get
Let two bodies move as shown in the figure. By the law of conservation of momentum,
Along x-axis-
Along y-axis-
By the law of conservation of kinetic energy
So along the line of impact (here along in the direction of ) We apply e
So we solve these equations
Work is the transfer of energy when a force is applied to an object, causing displacement. Energy, on the other hand, is the capacity to do work. The unit of work and energy is the joule (J).
The work-energy theorem states that the work done on an object is equal to the change in its kinetic energy.
This chapter introduces fundamental concepts that form the basis for understanding various physical phenomena. It helps explain how energy is transferred, how work is done, and how power is calculated in mechanical systems, making it essential for both academic exams and real-life applications.
Power helps quantify how quickly work is done or energy is transferred. Understanding power is crucial in practical scenarios, such as determining the efficiency of machines and engines or calculating the speed at which energy is consumed.
The concepts of work, energy, and power are foundational for various topics in competitive exams, especially mechanics and thermodynamics. Understanding these helps in solving a wide range of problems, improving both speed and accuracy in exams.
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