Work is the energy transfer that takes place when a force causes an object to move. Where: work done is measured in joules J force is measured in newtons N distance is measured in metres m.

What is the work done by the force to move the box 5 m?

NCERT Solutions for Class 9 Science Chapter 11

If the floor is smooth, where does this energy go? The box accelerates and gains kinetic energy. If the floor is rough, where does the energy go? Some or all of the energy is lost as heat and sound. This time, the box moves in a different direction to the direction of the applied force. How does this affect the work done? Can you think of any suggestions?

The tension in the rope can be broken down into a horizontal and a vertical component. The vertical component F does no work because Fsin the box does not move in that direction. Fcos So to calculate work done by a force at an angle:. Calculate the work done in pulling the toy if the tension in the string is 10 N, and it is pulled along 5 m.

Energy is the measure of the ability of an object or a system to perform work. There are many types of energy:. That energy might be: gravitational potential energy e. A bungee jumpers gravitational potential energy is changed into kinetic energy as they jump, and then stored as elastic potential energy as the bungee rope stretches.

Gravitational potential energy GPE, Ep or Egrav is the energy of an object due to its position in a gravitational field. The Ep gained by a mass is proportional to the force used to lift it, and the distance it is lifted:. How much gravitational potential energy does it gain? What is his gravitational potential energy at the highest point of his jump?

Different Forms Of Energy - Physics

Kinetic energy KE or Ek is the energy of an object due to its speed. For example, if an object of mass m is released above the ground at height h, it will gain speed, v, as it falls. Due to the conservation of energy, and assuming air resistance is negligible, after falling a height of h:.

What is the balls Ek as it is released? What is the balls maximum gain of Ep? The main resistive force is friction, which includes drag or air resistance. When an object such as a rollercoaster moves vertically without a driving force, any difference between a change in Ep and Ek corresponds to a loss of energy to resistive forces, or work done against resistive forces:.

Power is the rate at which work is done, or the rate at which energy is transferred. What is the power of the crane? At constant speed and height, the force produced by the powered object is equal but opposite to all resistive forces acting on the object, such as friction and air resistance.

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Efficiency is often expressed as a percentage. For example, what is the efficiency of a 60 W filament lamp that gives out 1 W of light?A lawn mower is pushed a horizontal distance of 20 m by a force of N directed at an angle of 30 o with the ground.

What is the work of this force? A student lifts a 50 pound lb ball 4 feet ft in 5 seconds s. How many joules of work has the student completed? Potential Energy Stored energy or gravitational energy. Energy transformation involves the conversion of one form of energy into another form. Examples of energy transformation include:. Now you know the basic forms of energy. A renewable energy source is a form of energy that is constantly and rapidly replenished by natural processes. Examples of renewable energy sources include:. Solar — The use of the sun as a source of heat; for instance, to heat a room within a house, etc. How much potential energy is lost by a 5Kg object to kinetic energy due a decrease in height of 4.

Potential energy of an object at a height An object increases its energy when raised through a height. The potential energy of an object at a height depends on the ground level or the zero level. The bigger unit of energy called kilowatt hour kW h 1 kW h is the energy used in one hour at the rate of J s—1 or 1 kW.

A 5 Kg Cart is pushed by a 30 N force against friction for a distance of 10m in 5 seconds.

Determine the Power needed to move the cart. A student lifts a How many watts of power are used to lift the ball? Important Points for Work Problems:.

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Two persons do the same amount of work. The first person does it in 10 s and the second, in 20 s. Find the ratio of the power used by the person to that by the second person. By what factor does the kinetic energy of an object depend on its direction of motion?

A body of mass 3. Calculate their Momenta, their Potential energies and kinetic energies when they are 10m above the ground. Who is delivering more power? Find the Ratio of power delivered by the man to that by the boy. Show that the work done by a force is given by the product of the force and the projection of the displacement along the force.

Find the expression for gravitational potential energy of a body of mass m at height h. Why does a person standing for a long time get tired when he does not appear to do any work? Please send your queries to ncerthelp gmail. The potential energy of an object at a height depends on the ground level or the zero level 4. Does work have a direction? Does the kinetic energy of an object depend on its direction of motion? Cam matter be converted into energy?Download revision notes for Work and Energy class 9 Notes and score high in exams.

These are the Work and Energy class 9 Notes prepared by team of expert teachers. The revision notes help you revise the whole chapter in minutes. Revising notes in exam days is on of the best tips recommended by teachers during exam days. Negative Work The friction force f opposes the displacement. Positive Work Force F contributes to displacement x.

Energy which a body possesses because of its motion, which occurs anywhere from an atomic level to that of a whole organism Examples of Kinetic Energy: This is not an all-inclusive list. Potential Energy Stored energy or gravitational energy. Energy transformation involves the conversion of one form of energy into another form.

Examples of energy transformation include:. There are renewable and nonrenewable sources of energy. A renewable energy source is a form of energy that is constantly and rapidly replenished by natural processes.

Solar — The use of the sun as a source of heat; for instance, to heat a room within a house, etc. Rate at which work is performed or energy is expended. Work and Energy class 9 Notes. CBSE quick revision note for Class-9 Science, Chemistry, Maths, Biology and other subject are very helpful to revise the whole syllabus during exam days.

The revision notes covers all important formulas and concepts given in the chapter. Even if you wish to have an overview of a chapter, quick revision notes are here to do if for you.

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These notes will certainly save your time during stressful exam days. Save my name, email, and website in this browser for the next time I comment. Download Now.Visit to Discussion Forum to share your knowledge or ask your doubts with our experts and your classmates. Potential energy of a body is by virtue of its position or shape whereas kinetic energy of a body is by virtue of its motion.

Internal combustion heat engines use the chemical energy of fossil fuels petrol and diesel for their operation. These engines first convert the chemical energy of the fuels into heat energy which is later on converted into mechanical energy. Answer 1: a J b 0. Question 2: A ball of mass 1 kg is dropped from a height of 5 m. Question 3: A man does J of work in 10 s and a boy does J of work in 4 s. A boy of mass 55 kg runs up a flight of 40 stairs, each measuring 0.

What is the difference between potential energy and kinetic energy? Why do some engines require fuels like petrol and diesel?

A porter lifts a luggage of 15 kg from the ground and puts it on his head 1.

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Calculate the work done by him on the luggage. A bullet of mass 20 g is found to pass two points 30 m apart in 4 s?

Energy, Work and Power Unit

Assuming the speed to be constant, find its kinetic energy. Two girls, each of weight N, climb up a rope through a height of 8 m. We name one girl A and the other girl B. Girl A takes 20 s while b takes 50 s to accomplished this task. What is the power expended by each girl? Important Questions on 9th Science Chapter 11 An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground.

The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object? So, the total work down is zero in throughout the motion. A battery lights a bulb. Describe the energy changes involved in the process. Battery converts chemical energy into electrical energy. This electrical energy is further converted into light and heat energy. A mass of 10 kg is at a point A on a table.

It is moved to a point B.In these notes a brief and simple explanation of all important topics is given which will help students make an easy and quick revision of the chapter during the examinations. Though these notes we bring a brief description of the important topics from chapter which will help you revise the whole chapter quickly and easily during exam days.

At the end of the notes you can try the questions asked from the discussed set of topics. These questions will help you to assess your preparation level and get a hold on the subject. It is expressed as the product of force and displacement in the direction of force. Necessary Conditions for Work to be done. Energy The capacity of a body to do work is called the energy of the body. The various forms of energy are potential energy, kinetic energy, heat energy, chemical energy, electrical energy and light energy. Let an object of mass mstarts from rest and attains a uniform velocity vafter a force F is applied on it. Let during this period the object be be displaced by distance s.

Potential Energy The energy possessed by a body due to its position or shape is called its potential energy. It states that energy can neither be created nor destroyed, but it can be transformed from one form to another.

Let a body of mass m falls from a point A, which is at a height h from the ground as shown in the following figure:. A body of mass 3. Calculate their Momenta, their Potential energies and kinetic energies when they are 10m above the ground. A light and heavy body have equal momenta. Which one has greater kinetic energy? Why does a person standing for a long time get tired when he does not appear to do any work?

Study at Home. School Board. Current Affairs.NCERT Solutions for class 9 Science provided herein are designed by our subject matter experts in a simple and precise manner. It covers answers to all the in between exercises and exercises given at the end of the chapter. The ideas and concepts presented through the solved numerical problems and solutions to the in between exercises will provide the learners a set of tools with which they can understand about the scientific concept of work.

The simple and comprehensible solutions will help the learner to understand the concept of Energy including how to forms of energy, kinetic energy. The learner can master the art of solving numerical problems by following and practicing the fully solved step by step explanations that serve as a guide. The solutions will provide an overview of the complete chapter bringing the key ideas into a clear perspective. Along with these concepts potential energy including potential energy of an object at a height, are various energy forms interconvertible?

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The solutions to the questions mentioned in between and at the end of the chapter are framed by our subject matter experts and comprises step by step answer to all the problems. Students are, therefore, advised to go through these solutions to know more about the fundamental principles and concepts of the topic involved and to score well in the exam.

The topics and sub-topics in Chapter 11 Work and Energy are given below. We cover all exercises in the chapter given below Download the free PDF of Chapter 11 Work and Energy and take the print out to keep it handy for your exam preparation.Whenever a force makes a body move, then work is said to be done.

But for doing work, energy is required. When work is done by human beings, machines or animals they get energy from the food which they eat and if work is done via machines, then energy is supplied by fuels or by electricity. So, we can say that when work is done an equal amount of energy is used up.

This article deals with the summary of Work, Power and Energyits mechanism, formulas and how they are related to each other in a crux form which not only clear your concepts but also help in your preparation and in solving problems. Work can be done when a force produces a motion. For e. Therefore, Work is measured by the product of force and displacement of the body along the direction of force.

It is a scalar quantity and its SI unit is joule. Note: The condition for a force to do work is that it should produce motion in an object, i. For example, if a man pushes a wall, but there is no displacement that is wall is stationary it does not move, then, the work done by the man on the wall is zero. But the work done on the body of the man himself is not zero. Because while pushing the wall man consumes energy, his muscles are stretched and he feels tired. Also, we can take another example that if a man stands still at a bus stop with heavy suitcase in his hand, he may get tired soon but he does no work in this situation because suitcase held by the man do not move at all.

So, it is clear now that whenever a force is applied to an object it is not necessary that work is done. Work is done when force able to move the object. What happens when work is done against gravity? Whenever work is done against gravity, the amount of work done is equal to the product of weight of the body and the vertical distance through which the body is lifted. Motion and Mechanics. Capacity of doing work by a body is called energy. Energy is a scalar quantity i.

The energy required to do 1 joule of work is called 1 joule energy. It is of two types:.

Work and Energy class 9 Notes Science

Source: www. Potential Energy : The capacity of doing work developed in a body due to its position or configuration or we can say that the energy of a body due to its position or change in shape.

Energy of compressed string, energy of water collected at a height, energy of spring in a watch etc. Kinetic Energy: The energy of a body due to its motion. So, it is clear from above formula that when momentum is doubled, kinetic energy becomes four times. Also, when work is done, an equal amount of energy is consumed. Thus, power is also defined as the rate at which energy is consumed or utilised. The S. I unit of power is watt W.

One watt is the power of an appliance which does work at the rate of 1 joule per second. Energy can neither be created nor destroyed. Only energy can be transformed from one form to another. Whenever energy is utilised in one form, equal amount of energy is produced in other form. Hence, total energy of the universe remains same.