NCERT Solutions for Class 9 Science Chapter 11 – Work and Energy

NCERT Solutions for Class 9 Science Chapter 11: Work and Energy will help you prepare topics like force, displacement, the direction of displacement, work and their mathematical formulae. The chapter deals with numerous other concepts like kinetic energy, potential energy, electric energy, power etc. Our NCERT Solutions for Class 9 explain all these concepts in detail for your reference. 

CBSE Class 9 NCERT Chapter 11 forms a very essential part of class 9 science syllabus. It has 5 exercises and 33 questions in total. These exercises aim at strengthening your knowledge about the concepts of the chapter. Preparing the solutions will, therefore, enable you to learn and apply concepts in different kinds of problems related to this chapter. 

Our NCERT solutions for class 9 science chapter 11 will also help you with concepts like the law of conservation of energy, conditions in which work is done, expressions of power and gravitational potential. these solutions adhere to the CBSE syllabus which will make it easier for you to prepare for your CBSE exams. Given below is a short summary of the chapter and a quick discussion on the exercise questions.

Important Topics of NCERT Solutions for Class 9 Chapter 11: Work and Energy


Unlike our general understanding of doing work, the chapter of NCERT Solutions for Class 9 Science Chapter 11 deals with an altogether different approach. In this chapter, you will study that work is said to be done only when the following two conditions are fulfilled

  1. A force acts on the body
  2. When there is a displacement which is caused in the body due to the force applied to it and this displacement is along the direction of the force applied. 

When force F displaces a body with a distance of s in the direction of this force then the work done W on the body is denoted by the expression 

W = F x s 


The rate of doing work is known as power. Power can also be defined as the rate of transfer of energy. If the amount of work done is denoted by W, and the time in which this work is done is denoted by t, then the expression for power will be written as 

Power = work / time 

Power = energy / time 

P = W / t 

Average Power 

A body is capable of doing different quantities of work in different time periods. Therefore the concept of average power is essential. The value of average power is obtained by dividing the total amount of work done by the total time which was taken to complete that work.

Average power = total work done/ total time taken. 

Change of energy in case of an object freely falling towards the ground

The chapter also deals with various kinds of energy changes while doing certain tasks. There are changes from electrical energy to heat energy, from heat energy to kinetic energy, from potential energy to kinetic energy etc. In case of a free-falling object, there are similar energy changes. When an object falls freely towards the ground, there is a change in its energy. All the potential energy that it carried gets changed into kinetic energy. As soon as the object crashes to the ground, all the kinetic energy that it carried, gets converted into heat and sound energy. 

Numerical problems 

The chapter has a considerable amount devoted to numerical problems. These are based on the concepts and formulas that have been dealt with and discussed in the chapter. 

Example –

Find the energy in KWh consumed in 10 hrs by four devices of power 500 W each. 

Solution –

Power = W/T 


Power rating of the device (give) = 500 W = 0.50 W 

Time for which the device rune (given) = T = 10 hrs

Work done = energy consumed by the device 

Therefore energy consumed by the device = Power x Time 

= 0.50 x 10 = 5 kWh 

Hence the energy consumed by four equal rating devices in 10 hours = 4 x 5 kWh = 20 kWh = 20 Units. 

Exercise-wise Discussion of NCERT Class 9 Solutions for Chapter 11 – Work and Energy

  1. Science NCERT Class 9 Chapter 11 ‘Work and Energy’ comprises of diverse categories of questions. These questions aim at testing your analyzing and observation skills which are the put to application. 
  2. The first exercise of NCERT Solutions Class 9 Chapter 11 – Work and Energy, is a simple numerical which is a great start to the conceptual practise for the further questions in the exercise. 
  3. Then there are theory-based questions like the one which asks “when do we say work is done”. There are also questions which require you to write expressions of the physical quantities and terms that have been introduced in the chapter. 
  4. The exercise also has questions which require diagrammatic representation, like the one which asks about the energy changes occurring at different points in a pendulum. 
  5. The numerical problems seek application skills. These problems make use of the formulas that you have learnt in the chapter. For instance, some numerical problems of the chapter require you to determine the energy, power, gravitational force etc. from the values and conditions given in the questions. 

About NCERT Solutions for Class 9 Chapter 11 – Work and Energy by Instasolv

If you are tired of rushing to tuitions for finding the right solutions to your doubts, Instasolv is the right place for you. Here, you can find step-wise solutions to all the NCERT questions for Class 9 science chapter 11 and get your doubts solved instantly. We ensure that once you have a look at our NCERT solutions, you will not require additional study material for NCERT Class 9 Science Chapter 11. With excellent solutions, no hurdle can come in your way of scoring high marks in CBSE class 9 science exams and improving your academics.