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Work Energy and Power One Shot Physics | Class 11 Physics NCERT Full Explanation with Ashu Sir

Science and Fun Education・140 minutes read

The text delves into the concepts of work, energy, and power in physics, covering formulas, calculations, and their applications. It emphasizes the importance of understanding dot and cross products, potential energy in different scenarios, and the conservation of energy in various systems.

Insights

Work in physics is defined as force causing displacement, with the formula being force multiplied by displacement, and it is a scalar quantity measured in Joules (J).
Understanding dot and cross products is crucial in work done calculations, with the angle between force and displacement vectors affecting the formula and requiring knowledge of vector mathematics.
Kinetic energy is defined as the energy of an object in motion, calculated as half the mass multiplied by the square of its velocity, and it is directly proportional to momentum.
Elastic collisions maintain kinetic energy before and after the collision, showcasing the exchange of velocities between identical bodies and the conservation of momentum.

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Recent questions

What is work in physics?
Work is force causing displacement, calculated as force multiplied by displacement.
What is kinetic energy?
Kinetic energy is the energy of an object in motion, calculated as half the mass multiplied by the square of its velocity.
What is potential energy?
Potential energy is the energy stored by a body due to a change in shape or state, classified into gravitational, elastic, and electrostatic potential energy.
What is the Law of Conservation of Energy?
The Law of Conservation of Energy states that energy cannot be created or destroyed, only transformed between different forms.
What is power in physics?
Power is the rate of doing work, measured in watts, with one watt equaling one joule of work done per second.

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Summary

00:00

Physics: Work, Energy, and Power Explained

Science and Fun Jahan But offers teaching with both heart and mind, focusing on one-shot series experiments.
The next recording covers the chapter on units, measuring motion in a straight line, motion in a plane, and laws of motion.
Due to exams and offline batch commitments, the one-shot series was delayed but has now resumed with work energy.
The chapter delves into work, energy, and power, with specific topics to cover.
Work is defined in physics as force causing displacement, with the formula being force multiplied by displacement.
Work is a scalar quantity, with the SI unit being Joules, represented by J.
Work done by constant force with force and displacement in the same direction follows a specific formula.
When force and displacement are not in the same direction, the work done formula involves resolving forces into components.
The angle between force and displacement vectors affects the work done formula, requiring understanding of dot and cross products.
The chapter emphasizes the importance of understanding dot and cross products for further comprehension.

13:52

Vector Products: Dot vs Cross, Work Calculations

Dot product and cross product are different meanings in vectors.
Dot product of two vectors results in a scalar quantity.
The formula for dot product is a.k.Theta.
Cross product of two vectors results in abs2.
Work done is calculated as f x d x cos(theta).
Work done is positive when the angle between force and displacement is acute.
Work done is negative when the angle between force and displacement is obtuse.
Work done is zero when force or displacement is zero, or when the angle is 90 degrees.
In circular motion, work done is zero due to perpendicular displacement and centripetal force.
Work done can be calculated for variable forces using integration.

27:56

"Displacement, Force, Work, Energy: Calculations Explained"

Displacement into k theta is now being discussed instead of Force, with a shift from constant force to variable force.
A very small displacement, denoted as d, is emphasized as being even smaller than imagined.
The concept of a very small displacement is reiterated, stressing its minuscule nature.
The force is expected to remain constant for smaller d, indicating a relationship between force and displacement.
The discussion delves into the integration of both sides to calculate work done, emphasizing the importance of numerical calculations.
The text explores scenarios where force is variable, leading to different cases of work done calculations.
The process of finding work done from 0 to 2 meters with a variable force is detailed, showcasing the integration of force and displacement.
The concept of the area under a force-displacement graph representing work done is introduced, highlighting its significance.
The transition from work done to energy is discussed, with kinetic energy being defined as the energy of an object in motion.
The formula for calculating kinetic energy is presented as half the mass of an object multiplied by the square of its velocity.

43:33

Relationship between Work, Kinetic Energy, and Momentum

The formula for kinetic energy is 1/2 mv2, where m is the mass of the object and v is the velocity squared.
The derivation of the formula involves two methods: using equations of motion and calculus (integration and differentiation).
Work done is calculated by force multiplied by displacement, which can be written as mass multiplied by acceleration.
The formula for work done is force multiplied by displacement, which can be written as 1/2 mv2.
The work done is converted into kinetic energy, as kinetic energy is the energy of a moving object.
The relationship between kinetic energy and momentum is that they are directly proportional to each other.
The momentum formula is derived by multiplying mass by velocity, showing a direct relationship with kinetic energy.
The work-energy theorem states that work done is equal to the change in kinetic energy of a body.
To change the kinetic energy of an object, work must be done on it, usually by applying force to increase its velocity.
The work-energy theorem is proven through derivations for both constant and variable forces, showing the relationship between work done and kinetic energy.

59:01

Energy and Forces: A Comprehensive Overview

Multiplying by mass on both sides gives the mass.
Multiplying by mass results in 1/2 mv1.
Kinetic energy final minus kinetic energy initial equals 1/2 av scr.
Work energy theorem states that work done equals change in kinetic energy.
Integration of force with respect to displacement gives work done for variable force.
Potential energy is energy stored by a body due to a change in shape or state.
Conservative forces store work done against them as potential energy.
Examples of conservative forces include gravitational, elastic, and electrostatic forces.
Non-conservative forces, like frictional and muscular forces, do not store work done against them.
Potential energy is classified into gravitational, elastic, and electrostatic potential energy based on the type of force worked against.

01:15:46

Understanding Potential Energy in Physics Curriculum

Potential energy is discussed in 11th class, with specific chapters to be read.
Gravitational potential energy is explained, emphasizing work against conservative forces.
The formula for work done against gravitational force is detailed.
The formula for potential energy is revisited from ninth grade.
The inaccuracy of the potential energy formula due to changing gravitational values is highlighted.
The concept that potential energy is independent of the path taken is explained.
Gravitational potential energy is linked to conservative forces.
The discussion shifts to potential energy in a spring, focusing on work against elastic forces.
The relationship between force, displacement, and spring constant is elaborated.
The impact of spring constant on the force required for displacement is emphasized.

01:32:11

Understanding Spring Constants and Energy Conservation

Spring constant is crucial in determining the behavior of springs.
The amount of force applied and the resulting displacement affect the spring constant.
Different types of springs are suitable for various uses based on their spring constant.
Springs with low spring constants are ideal for applications requiring minimal force.
Shock springs in vehicles illustrate the importance of spring constant in practical applications.
Potential energy in a spring is directly related to its spring constant and displacement.
The formula for spring constant (k) is derived from the force (f) and displacement (x).
Work done on a spring is converted into potential energy, following the formula 1/2 kx^2.
Elastic limit is the maximum deformation a spring can endure before permanent damage.
The Law of Conservation of Energy states that energy cannot be created or destroyed, only transformed between forms.

01:46:53

Pendulum Energy: Kinetic and Potential Dynamics

Main position in a pendulum can be defined in two ways: when it stops or oscillates back and forth.
Pendulum energy consists of kinetic and potential energy, with kinetic energy at extreme positions being zero.
At extreme positions A and B, the pendulum's velocity is zero, resulting in zero kinetic energy.
Kinetic energy is maximum at the mean position, where velocity is highest.
Total energy in a pendulum remains constant, with kinetic energy increasing as potential energy decreases.
Graphically, kinetic energy is zero at extreme positions and maximum at the mean position.
Potential energy is maximum at extreme positions and zero at the mean position.
The total energy graph represents the constant energy in a pendulum system.
In an experiment, if a pendulum's rope breaks at extreme positions, it falls straight down, while at the mean position, it follows a parabolic path.
Deriving the conservation of total energy in a pendulum system involves calculating kinetic and potential energy at different positions.

02:01:36

Energy Conservation in Collisions: Elastic vs Inelastic

Velocity at point b is crucial for determining kinetic energy.
Kinetic energy at point b is calculated as 1/2 m v^2.
Canceling out terms to simplify the kinetic energy calculation.
Total energy at point b is the sum of potential and kinetic energy.
Total energy at point b is represented by mg-1.
Total energy at point b confirms the conservation of energy.
Total energy at point C is also proven to be conserved.
Different types of collisions are discussed: elastic and inelastic.
Elastic collisions maintain kinetic energy before and after the collision.
Inelastic collisions result in a loss of kinetic energy.

02:18:08

Conservation of Momentum and Kinetic Energy in Collisions

Momentum before and after a collision is always equal, calculated as m1u1 + m2u2 = m1v1 + m2v2.
To simplify the equation, take m1(u1 - v1) and m2(v2 - u2) separately.
This equation applies to any type of collision due to the Law of Conservation of Momentum.
For elastic collisions, kinetic energy before and after remains equal, expressed as 1/2m1u1^2 + 1/2m2u2^2 = 1/2m1v1^2 + 1/2m2v2^2.
Simplifying further, m1(u1 - v1)^2 = m2(v2 - u2)^2, showing the exchange of kinetic energy.
The ratio of velocities before and after a collision, known as the coefficient of restitution, is crucial for elastic collisions.
For identical bodies colliding elastically, the exchange of velocities is evident, showcasing the impact of mass and velocity.
Velocity exchange occurs only between identical bodies in collisions, not between bodies of different masses.
Mathematically, the total momentum before and after a collision remains equal, as well as the kinetic energy.
The proof of velocity exchange in elastic collisions is demonstrated through the equations and simplifications of the momentum and kinetic energy equations.

02:34:37

Elastic Collisions, Power, and Two Dimensions

In elastic collisions, velocities are exchanged between bodies, leading to a transfer of momentum.
When two bodies collide, their velocities are exchanged, indicating an elastic collision.
The chapter discusses collisions in two dimensions, which may not be extensively covered in exams but are important for understanding.
Power is defined as the rate of doing work, measured in watts, with one watt equaling one joule of work done per second.
The formula for power can be derived as force multiplied by displacement over time, with one horsepower approximately equal to 746 watts or rounded to 750 watts.

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