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Work, Energy, and Simple Machines

Chapter 7. Work, Energy, and Simple Machines

This chapter introduces the fundamental concepts of work, energy, power and simple machines. It explains how a force performs work, how work is related to energy, different forms of energy, the principle of conservation of energy, and the role of simple machines in reducing human effort. The chapter connects scientific concepts with everyday activities such as walking, lifting objects, riding a bicycle, using machines and operating tools. 

Chapter Review

Chapter Overview

• Work – Work is done when a force causes an object to move in the direction of the applied force.
• Energy – Energy is the capacity of an object or a system to do work.
• Work-Energy Theorem – The work done on an object is equal to the change in its energy.
• Mechanical Energy – Mechanical energy is the sum of kinetic energy and potential energy.
• Kinetic Energy – Energy possessed by an object due to its motion.
• Potential Energy – Energy possessed by an object due to its position or configuration.
• Conservation of Mechanical Energy – In the absence of external losses, the total mechanical energy of a system remains constant.
• Power – Power is the rate at which work is done.
• Simple Machines – Devices that make work easier by changing the magnitude or direction of the applied force.
• Efficiency of Machines – Efficiency compares the useful work obtained with the total work supplied.

Key Concepts of the Chapter

• Scientific Meaning of Work – Work is done only when force produces displacement in its direction. 
• Formula of Work – Work (W) = Force (F) × Displacement (s).
• SI Unit of Work – Joule (J).
• Positive Work – Work is positive when force and displacement act in the same direction.
• Negative Work – Work is negative when force acts opposite to the displacement.
• Zero Work – Work becomes zero if there is no displacement, no force, or when force acts perpendicular to displacement. 
• Energy Transfer – Energy can be transferred through work, heat, radiation and electricity.
• Forms of Energy – Mechanical, Thermal, Light, Sound, Electrical, Chemical and Nuclear Energy. 
• Kinetic Energy Formula – K = ½mv².
• Potential Energy Formula – U = mgh.
• Mechanical Energy – Mechanical Energy = Kinetic Energy + Potential Energy.
• Power Formula – Power = Work ÷ Time.
• SI Unit of Power – Watt (W).
• Mechanical Advantage – Ratio of load lifted to the effort applied.
• Velocity Ratio – Ratio of distance moved by effort to the distance moved by load.
• Efficiency – Efficiency = (Useful Work Output ÷ Work Input) × 100%.

Important Formulae

Physical Quantity	Formula
Work	W = F × s
Kinetic Energy	K = ½mv²
Potential Energy	U = mgh
Mechanical Energy	ME = KE + PE
Power	P = W / t
Efficiency	(Useful Output Work ÷ Input Work) × 100%
Mechanical Advantage	MA = Load / Effort
Velocity Ratio	VR = Distance moved by Effort / Distance moved by Load

Important SI Units

Quantity	SI Unit
Work	Joule (J)
Energy	Joule (J)
Power	Watt (W)
Force	Newton (N)
Displacement	Metre (m)

Real-Life Applications

• Lifting Objects – Work is done against gravity while lifting a load.
• Moving Vehicles – Engines convert chemical energy into mechanical energy.
• Hydroelectric Plants – Water stored at height possesses potential energy which is converted into electrical energy.
• Sports – Running, jumping and throwing involve continuous conversion of energy.
• Simple Machines – Levers, pulleys, wheel and axle, inclined planes and screws reduce human effort.
• Daily Activities – Opening doors, cycling, climbing stairs and lifting school bags involve work and energy.

CBSE Competency Focus

• Identify situations where work done is positive, negative or zero.
• Apply work-energy theorem to solve numerical problems.
• Calculate kinetic and potential energy using the correct formula.
• Explain conservation of mechanical energy using real-life examples.
• Compare different forms of energy and their transformations.
• Analyse the working of simple machines in everyday life.
• Solve competency-based questions involving efficiency and mechanical advantage.

Chapter at a Glance

Force → Work → Energy → Work-Energy Theorem → Forms of Energy → Mechanical Energy → Kinetic Energy → Potential Energy → Conservation of Mechanical Energy → Power → Simple Machines → Mechanical Advantage → Velocity Ratio → Efficiency

ATP Education Exam Booster

Remember the scientific conditions for work, distinguish between positive, negative and zero work, learn all important formulae with SI units, understand the relationship between work and energy, practise numerical problems on kinetic and potential energy, and master the concepts of power, mechanical advantage, velocity ratio and efficiency. These topics are highly important for CBSE competency-based, case-study and numerical questions.

Work, Energy, and Simple Machines

Chapter 7. Work, Energy, and Simple Machines

This section introduces the scientific concept of work. In daily life, many activities are called work, but in science, work is done only when a force causes an object to move in the direction of the applied force. This page explains the meaning of work, the conditions required for work to be done, the formula of work, its SI unit, different types of work and their applications in everyday life. The concept forms the foundation for understanding energy and power. 

Work

In science, work is done only when a force acting on an object produces displacement in the direction of the applied force. Simply applying a force without causing displacement is not considered work.

Definition

Work is said to be done when a force applied on an object produces displacement in the direction of the force. 

Conditions for Work to be Done

• Application of Force – A force must act on the object.
• Displacement – The object must move from its original position.
• Direction of Force – The displacement should have a component in the direction of the applied force.

Scientific Formula

Work (W) = Force (F) × Displacement (s)

This formula is applicable when a constant force acts in the direction of displacement. 

SI Unit of Work

The SI unit of work is Joule (J).

One Joule

One joule of work is done when a force of 1 newton moves an object through a displacement of 1 metre in the direction of the applied force.

1 J = 1 N × 1 m 

Factors Affecting Work

• Magnitude of Force – Greater the applied force, greater the work done for the same displacement.
• Displacement – Greater the displacement in the direction of force, greater the work done.

Types of Work

• Positive Work – Work is positive when force and displacement are in the same direction.
• Negative Work – Work is negative when force acts opposite to the direction of displacement.
• Zero Work – Work becomes zero when there is no force, no displacement, or when the force acts perpendicular to the displacement. :contentReference[oaicite:4]{index=4}

Examples of Positive Work

• Pushing a Wheelchair – The applied force and displacement are in the same direction.
• Lifting a School Bag – The upward force moves the bag upward.

Examples of Negative Work

• Goalkeeper Stopping a Football – The applied force is opposite to the direction of motion of the ball.
• Applying Brakes on a Bicycle – The braking force acts opposite to the motion of the bicycle. 

Examples of Zero Work

• Pushing a Wall – Force is applied but the wall does not move.
• Carrying a Box Horizontally – The supporting force is vertical while the displacement is horizontal.

Force–Displacement Graph

For a constant force, the work done is equal to the area under the force–displacement graph. Even when the force changes, the area under the graph represents the total work done. 

Real-Life Applications

• Construction Work – Lifting bricks or cement bags involves mechanical work.
• Transportation – Engines perform work to move vehicles.
• Sports – Players perform work while kicking, throwing or lifting sports equipment.
• Machines – Cranes and elevators perform work by lifting heavy loads.

ATP Education Concept Builder

Many everyday activities are called work, but scientifically they may not involve work. For example, pushing a wall for several minutes makes you tired, yet no scientific work is done because the wall does not move. Always check whether force and displacement occur together before concluding that work has been done.

ATP Education Exam Booster

• Remember the three conditions required for work to be done.
• Learn the formula W = F × s and its SI unit.
• Differentiate clearly between positive, negative and zero work.
• Practise identifying work done in real-life situations.
• Remember that the area under a force–displacement graph represents the work done.
• CBSE competency-based questions often ask whether scientific work is done in everyday activities such as pushing a wall, carrying a bag or applying brakes.

Work, Energy, and Simple Machines

Chapter 7. Work, Energy, and Simple Machines

This section explains how work and energy are closely related. Whenever positive work is done on an object, it gains energy. The chapter also introduces the Work-Energy Theorem, different forms of energy, mechanical energy and kinetic energy. These concepts help us understand how energy changes from one form to another in everyday life. 

Energy

Energy is one of the most important physical quantities in science. Every activity, from walking to operating machines, requires energy. An object that can perform work is said to possess energy.

Definition

Energy is the capacity of an object or a system to do work. 

Characteristics of Energy

• Capacity to Do Work – Energy enables an object to perform work.
• Transferable – Energy can be transferred from one object to another.
• Convertible – Energy can change from one form into another.
• Conserved Quantity – Energy cannot be created or destroyed; it only changes form.

Work-Energy Theorem

The work done on an object appears as a change in its energy. This relationship is known as the Work-Energy Theorem.

Definition

Work Done on an Object = Change in its Energy

This theorem helps explain how applying a force changes the energy of an object. 

Importance of the Work-Energy Theorem

• Relates Work and Energy – It shows that work done produces a change in energy.
• Simplifies Calculations – Many motion problems can be solved using energy instead of forces.
• Explains Motion – It helps understand why moving objects gain or lose energy.

Transfer of Energy

Energy can move from one object to another in different ways.

Methods of Energy Transfer

• Mechanical Work – Energy is transferred when a force causes displacement.
• Heat – Energy flows from a hotter object to a colder object.
• Radiation – The Sun transfers energy to the Earth without direct contact.
• Electricity – Energy is transferred through electric circuits.
• Sound Waves – Vibrations transfer energy through a medium.

Energy exists in many different forms. One form of energy can be converted into another depending on the situation.

Major Forms of Energy

• Mechanical Energy – Energy due to motion or position of an object.
• Thermal Energy – Energy responsible for heating objects.
• Light Energy – Energy that enables us to see.
• Sound Energy – Energy carried by vibrations.
• Electrical Energy – Energy associated with electric charges.
• Chemical Energy – Energy stored in food, fuels and batteries.
• Nuclear Energy – Energy stored inside the nucleus of atoms.

Mechanical energy is the energy possessed by an object because of its motion or its position.

Definition

Mechanical energy is the sum of the kinetic energy and the potential energy of an object. 

Components of Mechanical Energy

• Kinetic Energy – Energy due to motion.
• Potential Energy – Energy due to position or configuration.

Kinetic Energy

Every moving object possesses kinetic energy. The faster an object moves or the greater its mass, the greater is its kinetic energy.

Definition

Kinetic energy is the energy possessed by an object due to its motion. 

Formula

K = ½mv²

SI Unit

The SI unit of kinetic energy is Joule (J). 

Factors Affecting Kinetic Energy

• Mass – Greater the mass, greater the kinetic energy.
• Velocity – Kinetic energy increases rapidly with velocity because it depends on the square of velocity.

Examples

• Moving Car – A moving car possesses kinetic energy.
• Rolling Ball – A rolling ball has kinetic energy due to its motion.
• Flying Cricket Ball – A fast-moving cricket ball carries kinetic energy.

ATP Education Concept Builder

Whenever work is done on an object, its energy changes. If positive work is done, the object's energy increases. If negative work is done, its energy decreases. Kinetic energy is present only when an object is in motion.

ATP Education Exam Booster

• Remember the definition of energy and the Work-Energy Theorem.
• Learn all major forms of energy with one example each.
• Memorise the formula K = ½mv².
• Remember that kinetic energy depends on both mass and the square of velocity.
• Practise numerical problems based on kinetic energy.
• CBSE frequently asks concept-based questions on the relationship between work, energy and motion.

Work, Energy, and Simple Machines

Chapter 7. Work, Energy, and Simple Machines

This section explains potential energy, mechanical energy, and the law of conservation of mechanical energy. It also describes how energy continuously changes from one form to another in nature and in everyday life. These concepts help us understand the working of pendulums, roller coasters, hydroelectric power stations and many other real-life systems.

Potential Energy

Potential energy is the energy possessed by an object because of its position or configuration. An object placed at a height stores energy due to the force of gravity.

Definition

Potential energy is the energy possessed by an object due to its position or shape.

Types of Potential Energy

• Gravitational Potential Energy – Energy stored because of the object's height above the ground.
• Elastic Potential Energy – Energy stored in stretched or compressed elastic objects such as springs and rubber bands.

Gravitational Potential Energy

When an object is lifted above the ground, work is done against gravity. This work is stored in the object as gravitational potential energy.

Formula

Potential Energy (PE) = m × g × h

Where

• m – Mass of the object (kg)
• g – Acceleration due to gravity (9.8 m/s²)
• h – Height above the ground (m)

SI Unit

The SI unit of potential energy is Joule (J).

Factors Affecting Potential Energy

• Mass – Greater the mass, greater the potential energy.
• Height – Greater the height, greater the potential energy.
• Gravity – Potential energy depends on the value of gravitational acceleration.

Examples of Potential Energy

• Water Stored in a Dam – Water at a height possesses gravitational potential energy.
• Book on a Shelf – The raised book stores potential energy.
• Stretched Rubber Band – Stores elastic potential energy.
• Drawn Bow – Energy is stored before releasing the arrow.

Mechanical Energy

Mechanical energy is the total energy possessed by an object because of its motion and position.

Definition

Mechanical energy is the sum of kinetic energy and potential energy.

Formula

Mechanical Energy = Kinetic Energy + Potential Energy

ME = KE + PE

Law of Conservation of Mechanical Energy

The total mechanical energy of an isolated system remains constant if no external force such as friction causes energy loss. Energy continuously changes between kinetic energy and potential energy, but the total remains the same.

Statement

Mechanical energy can neither be created nor destroyed. It only transforms from one form into another while the total mechanical energy remains constant.

Energy Transformation

Situation	Energy Conversion
Object Falling from a Height	Potential Energy → Kinetic Energy
Object Lifted Upward	Kinetic Energy → Potential Energy
Hydroelectric Power Plant	Potential → Kinetic → Electrical Energy
Bow and Arrow	Elastic Potential → Kinetic Energy
Roller Coaster	Potential ↔ Kinetic Energy

Applications of Mechanical Energy

• Hydroelectric Dams – Stored water produces electricity.
• Pendulums – Energy changes continuously between potential and kinetic forms.
• Roller Coasters – Height and speed keep changing while total mechanical energy remains nearly constant.
• Sports – Jumping, throwing and running involve continuous energy transformation.
• Windmills – Convert kinetic energy of moving air into electrical energy.

Difference Between Kinetic Energy and Potential Energy

Kinetic Energy	Potential Energy
Energy due to motion.	Energy due to position.
Depends on mass and velocity.	Depends on mass and height.
Formula: K = ½mv²	Formula: PE = mgh
Zero when the object is at rest.	Can exist even when the object is at rest.

ATP Education Concept Builder

Whenever an object moves upward, its kinetic energy gradually changes into potential energy. As it moves downward, the stored potential energy changes back into kinetic energy. This continuous conversion explains the conservation of mechanical energy.

ATP Education Exam Booster

• Remember the formula PE = mgh.
• Learn the difference between kinetic and potential energy.
• Understand the law of conservation of mechanical energy with real-life examples.
• Practise questions based on energy transformation.
• Hydroelectric plants, roller coasters and pendulums are important CBSE examples.

Work, Energy, and Simple Machines

Chapter 7. Work, Energy, and Simple Machines

This section explains power and simple machines, which make our daily work easier and more efficient. It also introduces the concepts of mechanical advantage, velocity ratio and efficiency. These ideas help us understand how machines reduce effort without creating energy. The concepts are widely used in engineering, construction, transportation and everyday life.

Power

Sometimes two people perform the same amount of work, but one completes it in less time than the other. The person who finishes the work more quickly is said to produce greater power.

Definition

Power is the rate at which work is done or energy is transferred.

Formula

Power (P) = Work Done (W) ÷ Time Taken (t)

P = W / t

SI Unit of Power

The SI unit of power is the watt (W).

1 Watt is the power produced when 1 joule of work is done in 1 second.

1 W = 1 J/s

Larger Units

• 1 kilowatt (kW) = 1000 W
• 1 megawatt (MW) = 1000 kW

Applications of Power

• Electric Motors – Higher power motors perform work faster.
• Vehicles – Powerful engines provide greater acceleration.
• Construction Machines – Cranes and excavators lift heavy loads quickly.
• Electrical Appliances – The power rating indicates the rate of energy consumption.

Simple Machines

A simple machine is a device that makes work easier by changing the magnitude or the direction of the applied force. Although machines reduce effort, they do not reduce the total work done.

Advantages of Simple Machines

• Reduce the effort required to perform work.
• Change the direction of the applied force.
• Increase the speed or distance of motion.
• Allow heavy objects to be lifted safely.
• Improve efficiency in everyday tasks.

Types of Simple Machines

Simple Machine	Common Examples
Lever	Seesaw, Crowbar, Bottle Opener, Scissors
Pulley	Well Bucket, Flagpole, Construction Crane
Wheel and Axle	Bicycle, Steering Wheel, Door Knob
Inclined Plane	Ramp, Staircase, Hill Road
Wedge	Knife, Axe, Chisel
Screw	Bolt, Screw Jack, Jar Lid

Mechanical Advantage (MA)

Mechanical advantage tells us how much a machine multiplies the applied effort.

Formula

Mechanical Advantage = Load ÷ Effort

MA = L / E

A larger mechanical advantage means less effort is required to lift or move a load.

Velocity Ratio (VR)

Velocity ratio compares the distance moved by the effort with the distance moved by the load.

Formula

Velocity Ratio = Distance moved by Effort ÷ Distance moved by Load

VR = DE / DL

Efficiency of a Machine

No machine is perfectly efficient because some energy is always lost due to friction, heat or sound.

Formula

Efficiency = (Useful Work Output ÷ Work Input) × 100%

Efficiency is always less than 100% for practical machines.

Real-Life Applications of Simple Machines

• Construction Sites – Cranes use pulleys to lift heavy materials.
• Hospitals – Wheelchairs use wheels and axles for smooth movement.
• Road Transport – Ramps help move heavy goods into vehicles.
• Agriculture – Farmers use levers and pulleys to reduce effort.
• Home Appliances – Bottle openers, scissors and screwdrivers are examples of simple machines.

Limitations of Machines

• Machines cannot create energy.
• Some energy is always lost due to friction.
• Regular maintenance is necessary for efficient working.
• A machine may reduce effort but can increase the distance through which the effort acts.

ATP Education Concept Builder

Remember that a machine does not reduce the total work done. It only changes how the work is performed. A machine may reduce the effort required, but the effort has to be applied over a greater distance. Therefore, simple machines make work easier and more convenient, not smaller.

ATP Education Classroom Examples

• Using a ramp to push a heavy box into a truck.
• Lifting a bucket from a well using a pulley.
• Opening a bottle with a bottle opener.
• Cutting paper using scissors.
• Turning a screw with a screwdriver.

ATP Education Exam Booster

• Learn the formula of power and its SI unit.
• Remember all six simple machines with examples.
• Understand Mechanical Advantage, Velocity Ratio and Efficiency.
• Know why no practical machine is 100% efficient.
• Practice identifying simple machines used in everyday life.
• CBSE competency-based questions often ask about the working principle and applications of simple machines.

Work, Energy, and Simple Machines

Chapter 7. Work, Energy, and Simple Machines

This section explains the conservation of mechanical energy, one of the most important principles in physics. As an object moves under the influence of gravity, its potential energy continuously changes into kinetic energy and vice versa. Although these two forms of energy keep changing, their sum remains constant when no external force such as friction acts on the object. This principle helps explain the motion of freely falling objects, pendulums, roller coasters and many other natural phenomena. 

Conservation of Mechanical Energy

Mechanical energy is the total energy possessed by an object due to its motion and position. It is equal to the sum of kinetic energy and potential energy.

Mechanical Energy

Mechanical Energy = Kinetic Energy + Potential Energy

ME = KE + PE

Law of Conservation of Mechanical Energy

When an object moves only under the influence of gravity and no external force such as friction acts on it, the total mechanical energy of the object remains constant. During motion, potential energy changes into kinetic energy and kinetic energy changes back into potential energy, but their total always remains the same. 

Mechanical Energy During Free Fall

Consider an object released from a height. As it falls towards the Earth, its height decreases while its speed increases.

Position of the Object	Potential Energy	Kinetic Energy	Mechanical Energy
Highest Point	Maximum	Zero	Constant
Middle Position	Decreases	Increases	Constant
Just Before Reaching the Ground	Minimum	Maximum	Constant

Energy Transformation During Free Fall

• At the Highest Point – The object possesses maximum potential energy and zero kinetic energy.
• During the Fall – Potential energy continuously converts into kinetic energy.
• Near the Ground – Almost all the potential energy changes into kinetic energy.
• Total Mechanical Energy – Remains constant throughout the motion if friction is neglected.

Why is Mechanical Energy Conserved?

Gravity does not destroy energy. It only converts one form of mechanical energy into another. Therefore, the total mechanical energy remains unchanged as long as no external force removes energy from the system.

Real-Life Applications

• Roller Coaster – Potential energy at the top changes into kinetic energy while moving downward.
• Pendulum – Energy continuously changes between kinetic and potential forms during oscillation.
• Hydroelectric Power Plant – Water stored at a height possesses potential energy which changes into kinetic energy and finally electrical energy.
• Waterfalls – Falling water converts gravitational potential energy into kinetic energy.
• Bungee Jumping – Energy changes repeatedly between kinetic and elastic potential energy.

Mechanical Energy Flow

Highest Point → Potential Energy → Kinetic Energy → Lowest Point

During the upward journey, the reverse process takes place.

Important Facts

• Mechanical energy is the sum of kinetic energy and potential energy.
• Mechanical energy is conserved only when external forces like friction are absent or negligible.
• Potential energy decreases as kinetic energy increases during free fall.
• Kinetic energy decreases while potential energy increases during upward motion.
• The SI unit of mechanical energy is the joule (J).

ATP Education Concept Builder

Students often think that potential energy disappears during free fall. In reality, it is simply converted into kinetic energy. The total mechanical energy remains constant throughout the motion, demonstrating the law of conservation of energy. This is one of the most important concepts for CBSE competency-based and numerical questions.

ATP Education Exam Booster

• Remember the formula: Mechanical Energy = KE + PE.
• Understand energy transformation during free fall.
• Learn the difference between kinetic energy, potential energy and mechanical energy.
• Practise identifying energy changes in roller coasters, pendulums and waterfalls.
• Remember that friction causes a part of the mechanical energy to convert into heat and sound energy.
• CBSE frequently asks conceptual questions based on the conservation of mechanical energy.

Work, Energy, and Simple Machines

Chapter 7. Work, Energy, and Simple Machines

This assignment is based on the complete chapter and follows the latest CBSE competency-based assessment pattern. It includes objective, descriptive, application-based, case-study and HOTS questions to strengthen conceptual understanding of work, energy, power and simple machines.

Chapter Assignment

1. One Word Answer

1. The capacity to do work.
2. The SI unit of work.
3. The SI unit of power.
4. Energy possessed due to motion.
5. Energy possessed due to position.
6. The product of force and displacement.
7. The law stating that energy can neither be created nor destroyed.
8. The quantity that measures the rate of doing work.
9. The ratio of load to effort.
10. A device that makes work easier.

2. Fill in the Blanks

1. Work is done only when force produces __________.
2. The SI unit of energy is __________.
3. Work = __________ × Displacement.
4. Kinetic energy depends on mass and __________.
5. The formula of potential energy is __________.
6. Mechanical energy is the sum of __________ and __________.
7. Power = __________ ÷ Time.
8. The SI unit of power is __________.
9. The efficiency of a machine is always __________ than 100%.
10. A pulley is an example of a __________ machine.

3. True or False

1. Pushing a wall without moving it is an example of scientific work.
2. One joule is equal to one newton metre.
3. Potential energy depends upon the height of the object.
4. Kinetic energy becomes zero when an object is at rest.
5. Mechanical energy always remains constant in the absence of friction.
6. Power and energy are the same physical quantities.
7. Simple machines create energy.
8. Mechanical advantage can be greater than one.
9. Efficiency of an ideal machine is 100%.
10. A ramp is an example of an inclined plane.

4. Match the Following

Column A	Column B
Work	Force × Displacement
Energy	Capacity to do work
Kinetic Energy	Energy due to motion
Potential Energy	Energy due to position
Power	Work done per unit time
Lever	Crowbar
Pulley	Draws water from a well
Wheel and Axle	Bicycle
Inclined Plane	Ramp
Screw	Bolt

5. Very Short Answer Questions

1. Define work.
2. State the conditions necessary for work to be done.
3. Write the formula for work.
4. Define energy.
5. What is kinetic energy?
6. What is potential energy?
7. State the law of conservation of mechanical energy.
8. Define power.
9. What is a simple machine?
10. Define mechanical advantage.

6. Short Answer Questions

1. Differentiate between positive, negative and zero work with suitable examples.
2. Explain the Work-Energy Theorem.
3. Describe the different forms of energy with examples.
4. Explain kinetic energy and the factors affecting it.
5. Explain potential energy with suitable examples.
6. Describe the conservation of mechanical energy during the free fall of an object.
7. Differentiate between kinetic energy and potential energy.
8. Explain the concept of power and its SI unit.
9. What are simple machines? Explain their importance in daily life.
10. Explain mechanical advantage, velocity ratio and efficiency.

7. Long Answer Questions

1. Explain the concept of work with its conditions, formula, SI unit and real-life applications.
2. Describe the different forms of energy and explain the relationship between work and energy.
3. Explain kinetic energy, potential energy and mechanical energy with suitable examples.
4. State and explain the law of conservation of mechanical energy using the example of a freely falling object.
5. Explain the concept of power and discuss its practical applications.
6. Describe different types of simple machines with suitable examples.
7. Explain mechanical advantage, velocity ratio and efficiency with appropriate diagrams or examples.
8. Discuss the importance of simple machines in transportation, construction and household work.

8. Case Study Questions

Case Study – 1

A worker pushes a heavy box across the floor. The box moves in the direction of the applied force.

1. Is work done in this situation?
2. Which two quantities determine the work done?
3. Write the formula for work.
4. Name the SI unit of work.

Case Study – 2

A ball is thrown vertically upward. It slows down, stops for a moment, and then falls back to the ground.

1. Which type of energy is maximum at the highest point?
2. Which type of energy is maximum just before reaching the ground?
3. Which law explains this change of energy?
4. What happens to the total mechanical energy (ignoring friction)?

Case Study – 3

A student climbs a staircase carrying a school bag to the first floor.

1. Which type of energy increases?
2. Has work been done? Give a reason.
3. Which force acts against the motion?
4. State the formula for potential energy.

Case Study – 4

A mechanic uses a pulley to lift a heavy engine.

1. Which simple machine is used?
2. Why is a pulley useful?
3. Define mechanical advantage.
4. Why is the efficiency of a practical machine less than 100%?

Case Study – 5

Two students lift the same object to the same height. One student takes less time than the other.

1. Did both students perform the same amount of work?
2. Which student produced greater power?
3. Define power.
4. Write its SI unit.

9. Competency-Based Questions

1. Why is no scientific work done while pushing a wall that does not move?
2. Explain why a fast-moving car possesses more kinetic energy than a slow-moving car.
3. Why does water stored in a dam have potential energy?
4. How does a roller coaster demonstrate the conservation of mechanical energy?
5. Why is power an important factor in selecting machines?
6. Explain why the efficiency of practical machines is always less than 100%.
7. How does an inclined plane reduce human effort?
8. Why do engineers use pulleys and levers in construction work?
9. Explain the energy transformations that occur in a hydroelectric power station.
10. Give two examples from daily life where simple machines make work easier.

10. HOTS Questions

1. A person carries a heavy suitcase on a horizontal road. Under what condition is scientific work considered zero? Explain.
2. Two objects have the same mass, but one moves twice as fast as the other. Compare their kinetic energies.
3. Why does the total mechanical energy remain constant during free fall even though kinetic and potential energies keep changing?
4. Can a machine reduce the total work done? Justify your answer.
5. Why is a longer ramp easier to use than lifting a load vertically?
6. Explain why a powerful motor can complete the same work in less time.
7. How would daily life be affected if simple machines did not exist?
8. A machine has a high mechanical advantage but low efficiency. Explain how this is possible.
9. Give one real-life example where energy changes through more than two forms before performing useful work.
10. Why are work, energy and power considered closely related physical quantities? Explain with suitable examples.