NEET Exam > NEET Notes > Physics Class 11 > Work, Energy & Power Class 11 Notes Physics Chapter 5
Work, Energy & Power Class 11 Notes Physics Chapter 5
| Download, print and study this document offline |
Please wait while the PDF view is loading
Page 1
Revision Notes
Class - 11 Physics
Chapter 6 – Work, Energy and Power
1. WORK
In Physics, work refers to ‘mechanical work’. Work is said to be done by a force
on a body when the body is actually displaced through some distance in the
direction of the applied force.
However, when there is no displacement in the direction of the applied force, there
is no work done, i.e., work done is zero, when displacement of the body in the
direction of the force is zero.
Consider a constant force ‘F’ acting on a body to produce a displacement ‘s’ in the
body along the positive x-direction as shown in the following figure:
If
?
is the angle which F makes with the positive x-direction of the displacement,
then the component of F in the direction of displacement is given by
Fco s ?
. Since
the work done by the force is the product of component of force in the direction of
the displacement and the magnitude of the displacement, we can write:
W (Fcos )s =?
Now, when the displacement is in the direction of force applied, i.e., when
0
0 ?=
;
( )
W Fcos0 s F .s ? = ? =
Page 2
Revision Notes
Class - 11 Physics
Chapter 6 – Work, Energy and Power
1. WORK
In Physics, work refers to ‘mechanical work’. Work is said to be done by a force
on a body when the body is actually displaced through some distance in the
direction of the applied force.
However, when there is no displacement in the direction of the applied force, there
is no work done, i.e., work done is zero, when displacement of the body in the
direction of the force is zero.
Consider a constant force ‘F’ acting on a body to produce a displacement ‘s’ in the
body along the positive x-direction as shown in the following figure:
If
?
is the angle which F makes with the positive x-direction of the displacement,
then the component of F in the direction of displacement is given by
Fco s ?
. Since
the work done by the force is the product of component of force in the direction of
the displacement and the magnitude of the displacement, we can write:
W (Fcos )s =?
Now, when the displacement is in the direction of force applied, i.e., when
0
0 ?=
;
( )
W Fcos0 s F .s ? = ? =
Clearly, work done by a force is the dot product of force and displacement.
In terms of rectangular components, F and s may be written as
x Y Z
ˆ ˆ ˆ
F iF jF kF = + + and
ˆ ˆ ˆ
s ix jy kz = + +
( ) ( ) x Y Z
ˆ ˆ ˆ ˆ ˆ ˆ
W iF jF kF . ix jy kz ? = + + + +
x y z
W xF yF zF ? = + +
Work is a scalar quantity, i.e., it has magnitude only and no direction. However,
work done by a force can be positive, negative or zero.
2. DIMENSIONS AND UNITS OF WORK
As work = force × distance;
1 2 2
W (M L T ) L
-
? = ?
1 2 2
W [M L T ]
-
?=
This is the dimensional formula of work.
The units of work are of two kinds: a) Absolute units and b) Gravitational units
a) Absolute units
1. Joule: It is the absolute unit of work in the SI system of units. Work done is
said to be one joule, when a force of one newton actually moves a body
through a distance of one meter in the direction of applied force.
0
1joule 1newton 1metre cos0 1N.m ? = ? ? =
2. Erg: It is the absolute unit of work in the CGS system of units. Work done is
said to be one erg, when a force of one dyne actually moves a body through
a distance of one cm in the direction of applied force.
0
1erg 1dyne 1cm cos0 1dyne.cm ? = ? ? =
Page 3
Revision Notes
Class - 11 Physics
Chapter 6 – Work, Energy and Power
1. WORK
In Physics, work refers to ‘mechanical work’. Work is said to be done by a force
on a body when the body is actually displaced through some distance in the
direction of the applied force.
However, when there is no displacement in the direction of the applied force, there
is no work done, i.e., work done is zero, when displacement of the body in the
direction of the force is zero.
Consider a constant force ‘F’ acting on a body to produce a displacement ‘s’ in the
body along the positive x-direction as shown in the following figure:
If
?
is the angle which F makes with the positive x-direction of the displacement,
then the component of F in the direction of displacement is given by
Fco s ?
. Since
the work done by the force is the product of component of force in the direction of
the displacement and the magnitude of the displacement, we can write:
W (Fcos )s =?
Now, when the displacement is in the direction of force applied, i.e., when
0
0 ?=
;
( )
W Fcos0 s F .s ? = ? =
Clearly, work done by a force is the dot product of force and displacement.
In terms of rectangular components, F and s may be written as
x Y Z
ˆ ˆ ˆ
F iF jF kF = + + and
ˆ ˆ ˆ
s ix jy kz = + +
( ) ( ) x Y Z
ˆ ˆ ˆ ˆ ˆ ˆ
W iF jF kF . ix jy kz ? = + + + +
x y z
W xF yF zF ? = + +
Work is a scalar quantity, i.e., it has magnitude only and no direction. However,
work done by a force can be positive, negative or zero.
2. DIMENSIONS AND UNITS OF WORK
As work = force × distance;
1 2 2
W (M L T ) L
-
? = ?
1 2 2
W [M L T ]
-
?=
This is the dimensional formula of work.
The units of work are of two kinds: a) Absolute units and b) Gravitational units
a) Absolute units
1. Joule: It is the absolute unit of work in the SI system of units. Work done is
said to be one joule, when a force of one newton actually moves a body
through a distance of one meter in the direction of applied force.
0
1joule 1newton 1metre cos0 1N.m ? = ? ? =
2. Erg: It is the absolute unit of work in the CGS system of units. Work done is
said to be one erg, when a force of one dyne actually moves a body through
a distance of one cm in the direction of applied force.
0
1erg 1dyne 1cm cos0 1dyne.cm ? = ? ? =
b) Gravitational units
These are also known as practical units of work.
1. Kilogram-meter (kg-m): It is the gravitational unit of work in the SI system
of units. Work done is said to be one kg-m, when a force of 1kgf moves a
body through a distance of 1m in the direction of the applied force.
0
1kg m 1kgf 1m cos0 9.8N 1m 9.8joules ? - = ? ? = ? = , i.e.,
1kg m 9.8J ? - =
2. Gram-centimeter (g-cm): It is the gravitational unit of work in the CGS
system of units. Work done is said to be one g-cm, when a force of 1gf
moves a body through a distance of 1cm in the direction of the applied force.
0
1g cm 1gf 1cm cos0 ? - = ? ?
1g cm 980dyne 1cm 1 ? - = ? ?
1g m 980ergs ? - =
3. NATURE OF WORK DONE
Although work done ( ) W (Fcos )s =? is a scalar quantity, its value may be
positive, negative, negative or even zero, as detailed below:
a) Positive work is said to be done on a body when
?
is acute (
0
90 ?
). Clearly,
cos ?
turns out to be positive and hence, the work done is positive.
For example, when a body falls freely under the action of gravity,
00
0 ;cos cos0 1 ? = ? = = + . Clearly, work done by gravity on a body falling
freely is positive.
b) Negative work is said to be done on a body when
?
is obtuse (
0
90 ?
).
Clearly,
cos ?
is negative and hence, the work done is negative.
For example, when a body is thrown up, its motion is opposed by gravity.
The angle
?
between gravitational force and the displacement is
0
180
. Since
0
cos cos180 1 ? = = -
; work done by gravity on a body moving upwards is
negative.
Page 4
Revision Notes
Class - 11 Physics
Chapter 6 – Work, Energy and Power
1. WORK
In Physics, work refers to ‘mechanical work’. Work is said to be done by a force
on a body when the body is actually displaced through some distance in the
direction of the applied force.
However, when there is no displacement in the direction of the applied force, there
is no work done, i.e., work done is zero, when displacement of the body in the
direction of the force is zero.
Consider a constant force ‘F’ acting on a body to produce a displacement ‘s’ in the
body along the positive x-direction as shown in the following figure:
If
?
is the angle which F makes with the positive x-direction of the displacement,
then the component of F in the direction of displacement is given by
Fco s ?
. Since
the work done by the force is the product of component of force in the direction of
the displacement and the magnitude of the displacement, we can write:
W (Fcos )s =?
Now, when the displacement is in the direction of force applied, i.e., when
0
0 ?=
;
( )
W Fcos0 s F .s ? = ? =
Clearly, work done by a force is the dot product of force and displacement.
In terms of rectangular components, F and s may be written as
x Y Z
ˆ ˆ ˆ
F iF jF kF = + + and
ˆ ˆ ˆ
s ix jy kz = + +
( ) ( ) x Y Z
ˆ ˆ ˆ ˆ ˆ ˆ
W iF jF kF . ix jy kz ? = + + + +
x y z
W xF yF zF ? = + +
Work is a scalar quantity, i.e., it has magnitude only and no direction. However,
work done by a force can be positive, negative or zero.
2. DIMENSIONS AND UNITS OF WORK
As work = force × distance;
1 2 2
W (M L T ) L
-
? = ?
1 2 2
W [M L T ]
-
?=
This is the dimensional formula of work.
The units of work are of two kinds: a) Absolute units and b) Gravitational units
a) Absolute units
1. Joule: It is the absolute unit of work in the SI system of units. Work done is
said to be one joule, when a force of one newton actually moves a body
through a distance of one meter in the direction of applied force.
0
1joule 1newton 1metre cos0 1N.m ? = ? ? =
2. Erg: It is the absolute unit of work in the CGS system of units. Work done is
said to be one erg, when a force of one dyne actually moves a body through
a distance of one cm in the direction of applied force.
0
1erg 1dyne 1cm cos0 1dyne.cm ? = ? ? =
b) Gravitational units
These are also known as practical units of work.
1. Kilogram-meter (kg-m): It is the gravitational unit of work in the SI system
of units. Work done is said to be one kg-m, when a force of 1kgf moves a
body through a distance of 1m in the direction of the applied force.
0
1kg m 1kgf 1m cos0 9.8N 1m 9.8joules ? - = ? ? = ? = , i.e.,
1kg m 9.8J ? - =
2. Gram-centimeter (g-cm): It is the gravitational unit of work in the CGS
system of units. Work done is said to be one g-cm, when a force of 1gf
moves a body through a distance of 1cm in the direction of the applied force.
0
1g cm 1gf 1cm cos0 ? - = ? ?
1g cm 980dyne 1cm 1 ? - = ? ?
1g m 980ergs ? - =
3. NATURE OF WORK DONE
Although work done ( ) W (Fcos )s =? is a scalar quantity, its value may be
positive, negative, negative or even zero, as detailed below:
a) Positive work is said to be done on a body when
?
is acute (
0
90 ?
). Clearly,
cos ?
turns out to be positive and hence, the work done is positive.
For example, when a body falls freely under the action of gravity,
00
0 ;cos cos0 1 ? = ? = = + . Clearly, work done by gravity on a body falling
freely is positive.
b) Negative work is said to be done on a body when
?
is obtuse (
0
90 ?
).
Clearly,
cos ?
is negative and hence, the work done is negative.
For example, when a body is thrown up, its motion is opposed by gravity.
The angle
?
between gravitational force and the displacement is
0
180
. Since
0
cos cos180 1 ? = = -
; work done by gravity on a body moving upwards is
negative.
c) Zero work is said to be done on a body when force applied on it or the
displacement caused or both of them are zero. Here, when angle
?
between
force and displacement is
0
90
;
0
cos cos90 0 ? = =
and hence, the work done
is zero.
For example, when we push hard against a wall, the force we exert on
the wall does no work because displacement is zero in this case. However, in
this process, our muscles are contracting and relaxing alternately and
internal energy is being used up. This is why we do get tired.
4. WORK DONE BY A VARIABLE FORCE
a) Graphical Method:
A constant force is rare. It is the variable force which is encountered more
commonly.
To evaluate the work done by a variable force, let us consider a force acting
along a fixed direction, say x–axis, but having a variable magnitude.
We have to compute work done in moving the body from A to B under the
action of this variable force.
To facilitate this, we assume that the entire displacement from A to B is
made up of a large number of infinitesimal displacements.
One such displacement shown in the following figure from P to Q.
Page 5
Revision Notes
Class - 11 Physics
Chapter 6 – Work, Energy and Power
1. WORK
In Physics, work refers to ‘mechanical work’. Work is said to be done by a force
on a body when the body is actually displaced through some distance in the
direction of the applied force.
However, when there is no displacement in the direction of the applied force, there
is no work done, i.e., work done is zero, when displacement of the body in the
direction of the force is zero.
Consider a constant force ‘F’ acting on a body to produce a displacement ‘s’ in the
body along the positive x-direction as shown in the following figure:
If
?
is the angle which F makes with the positive x-direction of the displacement,
then the component of F in the direction of displacement is given by
Fco s ?
. Since
the work done by the force is the product of component of force in the direction of
the displacement and the magnitude of the displacement, we can write:
W (Fcos )s =?
Now, when the displacement is in the direction of force applied, i.e., when
0
0 ?=
;
( )
W Fcos0 s F .s ? = ? =
Clearly, work done by a force is the dot product of force and displacement.
In terms of rectangular components, F and s may be written as
x Y Z
ˆ ˆ ˆ
F iF jF kF = + + and
ˆ ˆ ˆ
s ix jy kz = + +
( ) ( ) x Y Z
ˆ ˆ ˆ ˆ ˆ ˆ
W iF jF kF . ix jy kz ? = + + + +
x y z
W xF yF zF ? = + +
Work is a scalar quantity, i.e., it has magnitude only and no direction. However,
work done by a force can be positive, negative or zero.
2. DIMENSIONS AND UNITS OF WORK
As work = force × distance;
1 2 2
W (M L T ) L
-
? = ?
1 2 2
W [M L T ]
-
?=
This is the dimensional formula of work.
The units of work are of two kinds: a) Absolute units and b) Gravitational units
a) Absolute units
1. Joule: It is the absolute unit of work in the SI system of units. Work done is
said to be one joule, when a force of one newton actually moves a body
through a distance of one meter in the direction of applied force.
0
1joule 1newton 1metre cos0 1N.m ? = ? ? =
2. Erg: It is the absolute unit of work in the CGS system of units. Work done is
said to be one erg, when a force of one dyne actually moves a body through
a distance of one cm in the direction of applied force.
0
1erg 1dyne 1cm cos0 1dyne.cm ? = ? ? =
b) Gravitational units
These are also known as practical units of work.
1. Kilogram-meter (kg-m): It is the gravitational unit of work in the SI system
of units. Work done is said to be one kg-m, when a force of 1kgf moves a
body through a distance of 1m in the direction of the applied force.
0
1kg m 1kgf 1m cos0 9.8N 1m 9.8joules ? - = ? ? = ? = , i.e.,
1kg m 9.8J ? - =
2. Gram-centimeter (g-cm): It is the gravitational unit of work in the CGS
system of units. Work done is said to be one g-cm, when a force of 1gf
moves a body through a distance of 1cm in the direction of the applied force.
0
1g cm 1gf 1cm cos0 ? - = ? ?
1g cm 980dyne 1cm 1 ? - = ? ?
1g m 980ergs ? - =
3. NATURE OF WORK DONE
Although work done ( ) W (Fcos )s =? is a scalar quantity, its value may be
positive, negative, negative or even zero, as detailed below:
a) Positive work is said to be done on a body when
?
is acute (
0
90 ?
). Clearly,
cos ?
turns out to be positive and hence, the work done is positive.
For example, when a body falls freely under the action of gravity,
00
0 ;cos cos0 1 ? = ? = = + . Clearly, work done by gravity on a body falling
freely is positive.
b) Negative work is said to be done on a body when
?
is obtuse (
0
90 ?
).
Clearly,
cos ?
is negative and hence, the work done is negative.
For example, when a body is thrown up, its motion is opposed by gravity.
The angle
?
between gravitational force and the displacement is
0
180
. Since
0
cos cos180 1 ? = = -
; work done by gravity on a body moving upwards is
negative.
c) Zero work is said to be done on a body when force applied on it or the
displacement caused or both of them are zero. Here, when angle
?
between
force and displacement is
0
90
;
0
cos cos90 0 ? = =
and hence, the work done
is zero.
For example, when we push hard against a wall, the force we exert on
the wall does no work because displacement is zero in this case. However, in
this process, our muscles are contracting and relaxing alternately and
internal energy is being used up. This is why we do get tired.
4. WORK DONE BY A VARIABLE FORCE
a) Graphical Method:
A constant force is rare. It is the variable force which is encountered more
commonly.
To evaluate the work done by a variable force, let us consider a force acting
along a fixed direction, say x–axis, but having a variable magnitude.
We have to compute work done in moving the body from A to B under the
action of this variable force.
To facilitate this, we assume that the entire displacement from A to B is
made up of a large number of infinitesimal displacements.
One such displacement shown in the following figure from P to Q.
Since the displacement PQ dx = is infinitesimally small, we consider that all
along this displacement, force is constant in magnitude as well in the same
direction.
Now, a small amount of work done in moving the body from P to Q is given
by,
dW F dx (PS)(PQ) area of strip PQRS = ? = =
Therefore, the total work done in moving the body from A to B is given by
W dW ?=
?
W F dx ? = ?
?
Here, when the displacement is allowed to approach zero, then the number
of terms in the sum increases without a limit. And the sum approaches a
definite value equal to the area under the curve CD.
Thus, we may rewrite that
dx x
W lim F(dx)
?
?=
?
Read More97 videos|376 docs|102 tests |
FAQs on Work, Energy & Power Class 11 Notes Physics Chapter 5
| 1. What is work and how is it related to energy and power? |  |
Ans. Work is defined as the transfer of energy that occurs when a force is applied to an object and it causes the object to move in the direction of the force. In the context of physics, work is calculated by multiplying the force applied to an object by the distance the object moves. This work done on an object is directly related to the energy transferred to the object. Power, on the other hand, is the rate at which work is done or energy is transferred. It is calculated by dividing the amount of work done by the time taken to do the work.
| 2. How does the conservation of energy apply to work and power? | |
Ans. The conservation of energy states that energy cannot be created or destroyed, it can only be transferred or converted from one form to another. In the context of work and power, this means that the total amount of energy used to do work or transfer energy remains constant. For example, if a certain amount of work is done on an object, the energy used to do that work is transferred to the object in the form of kinetic energy. Similarly, in terms of power, the total power output is equal to the power input, as energy is conserved.
| 3. How can we calculate the amount of work done on an object? | |
Ans. The amount of work done on an object can be calculated by multiplying the force applied to the object by the distance the object moves in the direction of the force. This can be represented by the equation W = F × d, where W is the work done, F is the force applied, and d is the distance moved. The unit of work is joules (J).
| 4. What is the relationship between work, energy, and power? | |
Ans. Work, energy, and power are interconnected concepts in physics. Work is the transfer of energy that occurs when a force is applied to an object and it causes the object to move. Energy is the capacity to do work or transfer heat. Power, on the other hand, is the rate at which work is done or energy is transferred. The relationship between these three concepts can be represented by the equation Power = Work / Time, where Power is measured in watts (W), Work in joules (J), and Time in seconds (s).
| 5. How does the concept of power relate to everyday life? | |
Ans. The concept of power is relevant in various aspects of everyday life. For example, electrical appliances in our homes are rated in terms of their power consumption, which determines how much energy they use per unit of time. The power output of vehicles, such as cars and motorcycles, is an important factor in determining their performance. In industries, power is a crucial factor in determining the efficiency and productivity of machines and processes. Understanding power helps us make informed decisions about energy usage and efficiency in our daily lives.
About this Document
4.6K Views
4.74/5 Rating
Mar 16, 2026 Last updated
Document Description: Work, Energy & Power Class 11 Notes Physics Chapter 5 for NEET 2026 is part of Physics Class 11 preparation. The notes and questions for Work, Energy & Power Class 11 Notes Physics Chapter 5 have been prepared according to the NEET exam syllabus. Information about Work, Energy & Power Class 11 Notes Physics Chapter 5 covers topics like and Work, Energy & Power Class 11 Notes Physics Chapter 5 Example, for NEET 2026 Exam. Find important definitions, questions, notes, meanings, examples, exercises and tests below for Work, Energy & Power Class 11 Notes Physics Chapter 5.
Introduction of Work, Energy & Power Class 11 Notes Physics Chapter 5 in English is available as part of our Physics Class 11 for NEET & Work, Energy & Power Class 11 Notes Physics Chapter 5 in Hindi for Physics Class 11 course. Download more important topics related with notes, lectures and mock test series for NEET Exam by signing up for free. NEET: Work, Energy & Power Class 11 Notes Physics Chapter 5
Description
Full syllabus notes, lecture & questions for Work, Energy & Power Class 11 Notes Physics Chapter 5 - NEET | Plus exercises question with solution to help you revise complete syllabus for Physics Class 11 | Best notes, free PDF download
Information about Work, Energy & Power Class 11 Notes Physics Chapter 5
In this doc you can find the meaning of Work, Energy & Power Class 11 Notes Physics Chapter 5 defined & explained in the simplest way possible. Besides explaining types of Work, Energy & Power Class 11 Notes Physics Chapter 5 theory, EduRev gives you an ample number of questions to practice Work, Energy & Power Class 11 Notes Physics Chapter 5 tests, examples and also practice NEET tests
Related Searches
MCQs, Work, Exam, Semester Notes, Energy & Power Class 11 Notes Physics Chapter 5, Energy & Power Class 11 Notes Physics Chapter 5, Sample Paper, Important questions, Extra Questions, Summary, practice quizzes, Free, Energy & Power Class 11 Notes Physics Chapter 5, shortcuts and tricks, past year papers, pdf , Work, Viva Questions, study material, mock tests for examination, Objective type Questions, video lectures, Work, ppt, Previous Year Questions with Solutions;