Work Energy and Power- Topics, Notes, Books, FAQs

Edited By Team Careers360 | Updated on May 06, 2022 11:30 AM IST

You must have heard these terms work, energy, and power very frequently in your day to day life, like a barber cutting hair, a laborer lifting bricks and transporting them and a student studying are all said to be working. But here in physics, work is defined using very specific words and it has a very precise meaning. Similarly, a gymnast who can do a lot number of pull-ups we say that he/she has very good stamina or in other words, he/she has a good amount of energy. This means energy is something which tells about the capacity to do the work.

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Work Energy and Power Topics
Overview of Work Energy and Power
How to prepare Work Energy and Power
Notes for Work Energy and Power
Work Energy and Power- Books

In physics as well energy is related to work similarly but as already mentioned the definition of the word Work is very precise itself in Physics hence the definition of energy as well. We often come across the word Power as well, for example, the bodybuilder hit the punching bag with huge power, so in a very crude way, we could say that the rate of doing work is power. We could loosely correlate the physical definitions and physiological pictures. In this chapter, we would go in depth of the definitions and relations between these three physical quantities.

Work Energy and Power Topics

Work is done by a force (Both constant force and a variable force), conservation of mechanical energy, potential energy, kinetic energy, work-energy theorem, Potential energy of a spring, conservative and non-conservative forces, power

Overview of Work Energy and Power

This chapter is very important because it will test your knowledge of the previous two chapters namely, Kinematics, Laws of Motion and it will be also useful and crucial for you for solving questions from the next chapters namely System of Particles, Rotational Motion and to some extent gravitation.

Related topics,

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Here we will try to understand the definition of Work, Energy, and Power.

Work: It is defined as the product of the force applied to the object and the distance it travels in the direction which is parallel to the direction of the force. It is represented by the letter W. It is a scalar quantity. S.I. unit of work is N-m or J (joules). $W = \vec F. \vec d$

Energy: It is the capacity to do work, it has the same unit as work and also it is a scalar quantity. But energy exists in many forms like Kinetic energy, Potential energy, Thermal energy, Heat energy, etc, but here we will only talk about kinetic energy and potential energy. It is denoted by letter E.

Power: It is the rate of doing work or the rate of transferring energy, It is denoted by the letter P and its S.I. units are J/s or W (watts). $P =\frac{W}{t} = \frac{\Delta E}{t}$

You will also come across a very important theorem of this chapter, known as a work-energy theorem. This theorem states that the work done on the particle due to all types of forces equals to change in kinetic energy of the particles. Let’s understand this theorem with the help of an example.

Example - A bob-pendulum was hanging through a height ‘h’ from its equilibrium position as shown in the figure. How much velocity will it attain at its equilibrium position if it is dropped from the height ‘h’?

Solution - We will take the help of Work energy theorem for solving this problem. Assuming the mass of the bob is ‘m’. The force which is acting on the bob is a gravitational force due to its weight.

$\Delta W = \frac{1}{2}mv_{f}^{2} - \frac{1}{2}mv_{i}^{2}$ $\Rightarrow mgh = \frac{1}{2}mv_{f}^{2} - \frac{1}{2}mv_{i}^{2}$

Its initial velocity is zero, $v_{i} = 0 , v_{f} = v$

$\Rightarrow v = \sqrt{2gh}$

NCERT Notes Subject Wise Link:

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How to prepare Work Energy and Power

It is one of the basic and important chapters in mechanics because with the help of the concept used in this chapter you will be able to solve questions from other mechanics chapters as well. So for preparing this chapter, you need to remember the concept from laws of motion and you should be able to understand what kind of forces are acting on the particle. You should also understand how scalar product of the two vectors is operated and what is the significance of scalar product. Because work, energy, and power all are a scalar quantity.

Notes for Work Energy and Power

This chapter is more of a concept based chapter there is very little to memorize, hence practice is the key here for getting a good hold on this chapter.
Some questions of this chapter will involve the use of calculus and Scalar product of vectors, hence keep your basics strong.
Give a significant number of mock tests and make note of your progress.
It would be easy for you to solve questions if you can imagine what all forces are acting on the object and how.
Make a list of questions which you were not able to solve in the first attempt or you took a long time solving them, after a week or two solve them again.

NCERT Solutions Subject wise link:

NCERT Exemplar Solutions Subject wise link:

Work Energy and Power- Books

For this chapter, we would recommend you to first go through NCERT book and your Lab manual and solve questions from those chapters. Then you should solve questions from NCERT Exemplar book for a good hold on this chapter. If you want to test yourself for competitive exams, then you should read Understanding Physics by D.C. Pandey.