# 9th Class Physics: Chapter 6 Work and Energy Short Questions Answers

## 9th Class Physics: Chapter 6 Work and Energy Short Question Answers

We are providing all Students from 5th class to master level all exams preparation in free of cost. Now we have another milestone achieved, providing all School level students to the point and exam oriented preparation question answers for all science and arts students.

After Online tests for all subjects now it’s time to prepare the next level for Punjab board students to prepare their short question section here. We have a complete collection of all classes subject wise and chapter wise thousands questions with the right answer for easy understanding.

Here we are providing complete chapter wise Physics questions and Answers for the 9th class students. All the visitors can prepare for their 9th class examination by attempting below given question answers.

In this List we have included all Punjab boards and both Arts and Science students. These Boards students can prepare their exam easily with these short question answer section

Lahore Board 9th classes short questions Answer

Rawalpindi Board 9th classes short questions Answer

Gujranwala Board 9th classes short questions Answer

Multan Board 9th classes short questions Answer

Sargodha Board 9th classes short questions Answer

Sahiwal Board 9th classes short questions Answer

DG Khan Board 9th classes short questions Answer

Bahwalpur Board 9th classes short questions Answer

All above mention Punjab Boards students prepare their annual and classes test from these online test and Short question answer series. In coming days we have many other plans to provide all kinds of other preparation on our Gotest website.

How to Prepare Punjab Board Classes Short Question Answer at Gotest

• Just Open the desired Class and subject which you want to prepare.
• You have Green bars which are Questions of that subject Chapter. Just click on Bar, it slides down and you can get the right answer to those questions.
• You can also Rate those question Answers with Helpful or not to make it more accurate. We will review all answers very carefully and also update time to time.

Now you can start your preparation here below

Define work. What is its SI unit?

Work: Work is said to be done when a force acting on a body displaces it in the direction of the force.

Work = Force x distance

SI unit of work: SI unit of work is joule (J)

Definition of Joule: The amount of work is one joule when a force of one newton displaces a body through one meter in the direction of force.

When does a force do work? Explain.

When force acting on a body displaces it through some distance S in the direction of force as shown in the given figure, it does work on a body.

Sometimes the force and displacement do not have the same direction such as shown in the figure.

In this case, force F is making an angle (θ) with the surface on which body is moved. Resolving F into its perpendicular components Fx and Fy as;

Fx = Fcosθ

Fy = Fsinθ

In case when force and displacement are not parallel then only the x-component Fx parallel to the surface causes the body to move on the surface and the y-component Fy.

Hence W = F x S

W = (Fcosθ)S

W = FS cosθ

Why do we need energy?

Energy used by us to perform many activities of life.

Energy is necessary for running and walking for humans.

Define energy; give two types of mechanical energy.

A body possesses energy if it is capable to do work.

Types of mechanical energy: Mechanical energy has two following types.

(i) Kinetic energy (ii) Potential energy

Kinetic energy: The energy possessed by a body due to its motion is called its kinetic energy.

Formula: K.E = ½(mv2)

Unit of kinetic energy is joule (J).

Potential energy: The ability of a body to do work due to its position is known as its potential energy.

Formula: P.E = mgh.

Unit of potential energy is joule (J).

Define K.E and derive its relation.

Kinetic Energy: The energy possessed by a body due to its motion is called its kinetic energy.

Formula of K.E can be proved as: Consider a body of mass m moving with velocity v. The body stops after covering some distance S due to some opposing force such as force of friction acting on it.

The body possesses kinetic energy and is capable to do work against opposing force F until all of its kinetic energy is used up.

As we know, Kinetic energy of the body = Work done by it due to motion

1. E = Force x displacement

K.E = F x S —————- (1)

In this case

Vi = v

Vf = 0

According to Newton’s second law of motion:

F= ma

a = –

In the given case, the motion is opposed, hence (a) is negative.

According to 3rd equation of motion:

2aS =

2(-F/m)S = (0)2 – (v)2

2(-FS/m) = -(v)2

2(-FS/m) = -v2

Both sides of equation have minus sign, so these signs are cancelled out. So,

2 = v2

FS =1/2mv2 ————- (2)

From eq (1) and (2) following relation can be obtained.

K.E = K.E = ½(mv2) ——— (3)

Eq (3) gives the kinetic energy possessed by a body of mass m moving with velocity v.

Define Potential energy and drive its relation.

Potential Energy: The ability of a body to do work due to its position is known as its potential energy.

P.E =mgh this relation can be proved as: Consider a body of mass m. Let it be raised through height h from the ground. The body will acquire potential energy equal to the work done in lifting it to height h.

Mass of the body = m

Force lifting the body = F= w = mg

Height attained = S = h

Work done on the body = W = FS

As we know, Fore = Weight, Distance = height

F = w, S=h

So

Work done on the body on the body = W = w x h ——– (1)

According to the formula of weight

Weight = mass x gravitational acceleration

w= mg

By putting the value of weight in eq (1)

Work done on the body = W= mgh

The work done W in raising the body to height h appears as its potential energy.

Potential energy of the body = mgh

P.E = mgh.

Thus, the potential energy possessed by the body with respect to the ground is mgh and is equal to the work done in lifting it through height h.

Why fossil fuels called non-renewable form of energy?

The fossil fuels take million of years for their formation. So these are known as non-renewable resources.

Which form of energy is most preferred and why?

Solar energy is most preferred energy because Sunlight does not pollute the environment in any way.

Solar energy reaching Earth is thousand times more than the energy consumption of mankind.

How is energy converted from one form to another? Explain.

Energy cannot be destroyed however it can be converted from one form to another form. But total energy of the system at any time remains constant.

For Example: By rubbing hands quickly, these will be warmed. Its mean in rubbing hands muscular energy is used and as a result heat is produced.

In this process of rubbing hands, mechanical energy is converted into heat energy.

The given figure shows interconversion of kinetic energy to potential energy and potential energy into kinetic energy.

At the surface of the earth, the potential energy of the body will be zero while at this point its kinetic energy is maximum.

At the highest point, the kinetic energy of the body will be zero while its potential energy is maximum at this point.

Name any five devices that convert electrical energy into mechanical energy.

1. Juicer, 2. Electric motor, 3. Electrical grinder, 4. Electric spinner, 5. Washing machine

Name a device that converts mechanical energy into electrical energy.

Generator is a device that converts mechanical energy into electrical energy.

What is meant by the efficiency of a system?

Efficiency of a system is the ratio of required form of energy obtained from a system as output to the total energy given to it as input.

How can you find the efficiency of a system?

Efficiency of a system can be found out by following formula.

Efficiency = required form of output/ total input energy

%Efficiency = (required form of output/total input energy) x 100

What is meant by the power?

Power is defined as the rate of doing work.

Power = work done/time taken

P = W/t

The unit of power is watt. Bigger units of power are kilowatt (kW), megawatt (MW) etc.

Define watt.

The power of body is one watt if it does work at the rate of 1 joule per second (1Js-1).

What is the unit of work? Define it.

SI unit of work: SI unit of work is joule (J).

Joule: The amount of work is one joule when a force of one Newton displaces a body through one meter in the direction of force.

Thus, 1J = 1N x 1m

A man has pulled a cart through 35m applying a force of 300N. Find the work done by the man.

Data: Distance = S = 35m

Force = F = 300N

Required: Work done =?

Formula: W = F x S

Work = Force x distance

Sol: By putting the values in the formula amount of work can be found out.

W = F xS

W = 35 x 300

W = 10500 J

The required work done by the man is 10500J.

Define energy and write names of its different types.

Energy: A body possesses energy if it is capable to do work.

Types of energy: Energy exists in various types which are given below:

1. Mechanical energy, 2.Heat energy, 3. Light energy, 4. Sound energy, 5, Electrical energy, 6.Chemical energy, 7.Nuclear energy

Define kinetic energy also write its equation.

Kinetic Energy: The energy possessed by a body due to its motion is called its kinetic energy.

Equation: K.E = ½(mv2)

A stone of mass 500g strikes the ground with velocity of 15ms-1. How much is kinetic energy of stone at the time it strikes the ground.

Sol. Mass of stone = m = 500g =0.5kg

Velocity = v= 15ms-1

K.E =?

We know that

K.E = ½(mv2)

= ½(0.5 x (15)2)

K.E = ½(0.5 x 225) = 56.25J

Geothermal well can be built by drilling deep near hot rocks at places, where magma is not very deep.

The kinetic energy of a body of mass 2kg is 25J. Find its speed.

Sol. Mass =m= 2kg

K.E. = K.E. = 25J

Speed =V=?

We know that

K.E = ½(mv2)

25 = ½(2)v2

V2 = 25

V =5ms-1

A car weighting 12kN has speed of 20ms-1. Find its Kinetic energy.

Sol. Weight = w = 12kN

Speed = v = 20 ms-1

Required: Kinetic energy = K.E=?

Formula: K.E = mv2

Solution: Value of K.E can be found out by using above formula

Weight = 12kN

As we know;

w = mg

w/g =m

12k/10 = m

m = 1.2kg

K.E = mv2

K.E = (1.2)(20)2

K.E = (1.2)(400)

K.E = 480

K.E = 240J

The required K.E of the car is 240kJ.

A body of mass 0.5kg strikes the ground with the velocity of 20ms-1. Find its Kinetic energy.

Sol. Mass = m = 0.5kg

Velocity = v= 20ms-1

K.E =?

We know that

K.E = mv2

K.E = (0.5)(20)2

K.E = (0.5)(400) = 100J

Thus, the K.E. of the stone is 100J as it strike the ground.

Define potential energy and write is formula.

Potential energy: The ability of body to do work due to its position is known as its potential energy.

Formula: P.E = mgh

A body of 50kg is raised to a height of 3m. Find its potential energy.

Sol. m = 50kg

h = 3m

g = 10ms-2

We know that

P.E. = mgh

P.E. = 50 x 10 x 3 = 1500J

Differentiate between sound energy and mechanical energy.

Sound Energy: Sound is a form of energy.

Sound is produced when a body vibrates.

Following instruments produce sound.

1. Vibrating diaphragm of a drum.
2. Vibrating strings of a sitar.
3. Vibrating air column of wind instruments such as flute pipe etc.
4. When a door is knocked, a sound is produced.

Mechanical energy: The energy possessed by a body both due to its motion or position is called mechanical energy.

Examples: Water running down a stream, wind, a moving car, a lifted hammer, a stretched bow, a catapult or a compressed spring etc. possesses mechanical energy.

Define Work and give its equation.

Work: Work is said to be done when a force acting on a body displaces it in the direction of the force.

Work = Force x Distance

Write the name of major sources of energy.

Major sources of energy: There are basically two major sources of energy.

1. Fossil Fuels 2. Nuclear Fuels

How Chemical Energy is obtained?

Chemical energy is present in food, fuels and in other substances. The energy is released from these substances during chemical reactions.

How mechanical energy change into heat energy?

Energy cannot be destroyed however it can be converted from one form to another form. But total energy of the system at any time remains constant.

By rubbing hands quickly, these will be warmed. Its mean in rubbing hands muscular energy is used and as a result heat is produced.

In this process of rubbing hands, mechanical energy is converted into heat energy.

Differentiate between mechanical and chemical energy.

Mechanical energy: The energy possessed by a body both due to its motion or position is called mechanical energy.

Examples: Water running down a stream, wind, a moving car, a lifted hammer, a stretched bow, a catapult or a compressed spring etc. possesses mechanical energy.

Chemical Energy: Chemical energy is present in food, fuels and in other substances. The energy is released from these substances during chemical reactions.

What is Bio mass and how energy is produced from it?

Biomas: Biomass is plant or animal wastes that can be burnt as fuel.

When animal dung, dead plants and dead animals decompose, they give off a mixture of methane and carbon dioxide which is used to generate electricity.

Write down the names of kind of Mechanical Energy.

Mechanical energy has two following types.

• Kinetic Energy
• Potential Energy

Describe the difference between electrical energy and light energy.

Electrical energy:

Electricity is one of the widely used form of energy.

Electrical energy can get form batteries and electric generators. Most of the electric generators are run by hydro power, thermal or nuclear power.

Light energy:

Light is an important form of energy.

Sun is the great source of light energy.

Light energy can be obtained from candles, electric bubs, fluorescent tubes and also by burning fuel.

What are environmental problems and why are they created?

Environmental problems such as pollution that consist of noise, air pollution and water pollution may arise by using different sources of energy such as fossil fuel and nuclear energy.

What is the use of solar cells?

Uses of solar cells:

Solar cells provide power to telephone booths, light houses and scientific research centers.

Solar cells are also used to power satellites.

Define sound energy.

Sound Energy: Sound is a form of energy. Sound is produced when a body vibrates.

Define electrical energy and sound energy:

Electrical energy: Electricity is one of the widly used form of energy. Electrical energy can be supplied through wires, easily to any derired place.

Sound energy: Sound is a form of energy. Sound is produced when a body vibrates.

How energy is produced by nuclear fuel? Explain.

The process taking place in nuclear reactors is known as nuclear fission. During fission reaction, the heavy nucleus of an atom splits up into smaller parts releasing a large amount of energy. Nuclear power plants give out a lot of nuclear radiations and vast amount of heat.

Write the name of any two non renewable and renewable sources of energy.

Non-renewable Resources: 1. Fossil fuels 2. Nuclear fuels

Renewable Resources: 1. Solar energy 2. Water power

Which form of energy is most preferred and why?

Solar energy is most preferred energy because Sunlight does not pollute the environment in any way.

What is meant by non-renewable source? Write an example.

Non-renewable source: The fossile fuels took millions of years for their formation, so, they are known as non-renewable resources.

For example: Oil, gas, coal.

Write the names of the parts of Solar Heating System.

A heating system consists of

1. A collecter 2. A storage device 3. A distribution system

Write two Renewable Energy Sources. Explain one of them shortly.

1. Energy from water
2. Energy from sun

Energy from water: Energy from water power is very cheap. Water power is becoming more popular. For water power dams are being constructed at suitable location in different parts of the world.

Write down the equation of Einstein and value of c.

The relation between mass and energy is given by Einstein mass energy equation:

E=mc2

Here c is the speed of light.

Its value is 3 x 108 ms-1

How can every citizen be helpful in controlling air pollution?

Every citizen can be helpful in controlling air pollution by sharing rides and using public transport, due to this less fuel and energy is used and less pollutant are released in the environment.

Write the uses of wind energy.

Uses of Wind energy:

1. Wind energy has powered sailing ships across the oceans.
2. Wind energy has been used by windmills to grind grain and pump water.
3. More recently, wind power is used to turn wind turbines.

Write two disadvantages of thermal pollution.

• Thermal pollution upsets the balance of life.
• Thermal pollution endangers the survival of many species.

Define nuclear energy.

Nuclear energy: Nuclear energy is the energy released in the form of nuclear radiations in addition to heat and light during nuclear fission and fusion reactions.

What is meant by solar cells?

Solar Cells: Solar energy can also be converted directly into electricity by solar cells.

By defining magma, describe geothermal energy.

There is hot molten part, deep in the Earth called magma. Water reaching close to the magma changes to steam due to the high temperature of magma. This energy is called geothermal energy.

How can we produce electricity by using of animal dung?

When animal dung, dead plants and dead animals decompose, they give off a mixture of methane and carbon dioxide. Electricity can be generated by burning methane.

Define Mechanical Energy.

Mechanical Energy: The energy possessed by a body both due to its motion or position is called mechanical energy.

Examples: Water running down a stream, wind, a moving car, a lifted hammer, a stretched bow, a catapult or a compressed spring etc. possesses mechanical energy.

Why fossil fuels are known as non-renewable sources?

The fossil fuels take millions of years for their formation. So these are known as non-renewable resources.

How energy is converted from one form to another? Explain.

Energy cannot be destroyed however it can be converted from one form to another form. But total energy of the system at any time remains constant.
By rubbing hands quickly, these will be warmed. Its mean in rubbing hands muscular energy is used and as a result heat is produced.
In this process of rubbing hands, mechanical energy is converted into heat energy.

Name any four devices that convert electrical energy into mechanical energy.

• Juicer
• Electric motor
• Electrical grinder
• Electric spinner

Write two disadvantages of fossil fuels.

Once the supply of fossil fuels is exhausted, the world would face serious energy crisis.

Fossil fuels would not be able to meet our future energy demands.

Exhausted supply of fossil fuels would cause serious social and economical problems for countries like us.

What is meant by efficiency of a system?

Efficiency of a system: Efficiency of a system is the ratio of required form of energy obtained from a system as output to the total energy given to it as input.

Formula of efficiency: Efficiency can be obtained by following formula.

Efficiency = required form of output/Total input energy

Efficiency is a ratio between two quantities writes their names.

Efficiency of a system is the ratio of required form of energy obtained from a system as output to the total energy given to it as input.

Define power and write its formula.

Power is defined as the rate of doing work.

Power = work done/time taken

P = W/t

Define watt.

Watt: The SI unit of power is watt.

The power of body is one watt if it does work at the rate of 1 joule per second (1Js-1).

Define watt and write how much watt is equal to one horse power?

Watt: The power of body is one watt if it does work at the rate of 1 joule per second (1Js-1).

1 horse power = 1 hp =746 watt

If a body does 11200 joule work in 10 seconds, find the power.

Work = w = 11200 J

Time = t = 10 sec

Power = p = ?

We know that

P = w/t = 11200/10

P = 1120 watt

A machine does 20 joule work in 4 seconds. Find its power.

Work = W = 20 J

Time = t = 4 sec

Power = P =?

We know that

P = W/t

P = 20/4 = 5 watt

Construct the energy converter flow diagram of an electric lamp.

You Can Learn and Gain more Knowledge through our Online Quiz and Testing system Just Search your desired Preparation subject at Gotest.
error: