Selina Textbook Solutions: Machines | Physics Class 10 ICSE PDF Download

 Page 1


Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE- 3 (A) 
 
Question 1: 
What do you understand by a simple machine? 
Solution 1: 
A machine is a device by which we can either overcome a large resistive force at some point by 
applying a small force at a convenient point and in a desired direction or by which we can obtain 
a gain in the speed. 
 
 
Question 2: 
State four ways in which machines are useful to us? 
Solution 2: 
Machines are useful to us in the following ways: 
(1) In lifting a heavy load by applying a less effort. 
(2) In changing the point of application of effort to a convenient point. 
(3) In changing the direction of effort to a convenient direction. 
(4) For obtaining a gain in speed. 
 
 
Question 3: 
Name a machine for each of the following use: 
(a) to multiply force 
(b) To change the point of application of force 
(c) To change the direction of force 
(d) To obtain gain in speed 
Solution 3: 
(a) To multiply force: a jack is used to lift a car. 
(b) To change the point of application of force: the wheel of a cycle is rotated with the help of a 
chain by applying the force on the pedal. 
(c) To change the direction of force: a single fixed pulley is used to lift a bucket full of water 
from the well by applying the effort in the downward direction instead of applying it upwards 
when the bucket is lifted up without the use of pulley. 
(d) To obtain gain in speed: when a pair of scissors is used to cut the cloth, its blades move 
longer on cloth while its handles move a little. 
 
 
Question 4: 
What is the purpose of a jack in lifting a car by it? 
 
 
Page 2


Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE- 3 (A) 
 
Question 1: 
What do you understand by a simple machine? 
Solution 1: 
A machine is a device by which we can either overcome a large resistive force at some point by 
applying a small force at a convenient point and in a desired direction or by which we can obtain 
a gain in the speed. 
 
 
Question 2: 
State four ways in which machines are useful to us? 
Solution 2: 
Machines are useful to us in the following ways: 
(1) In lifting a heavy load by applying a less effort. 
(2) In changing the point of application of effort to a convenient point. 
(3) In changing the direction of effort to a convenient direction. 
(4) For obtaining a gain in speed. 
 
 
Question 3: 
Name a machine for each of the following use: 
(a) to multiply force 
(b) To change the point of application of force 
(c) To change the direction of force 
(d) To obtain gain in speed 
Solution 3: 
(a) To multiply force: a jack is used to lift a car. 
(b) To change the point of application of force: the wheel of a cycle is rotated with the help of a 
chain by applying the force on the pedal. 
(c) To change the direction of force: a single fixed pulley is used to lift a bucket full of water 
from the well by applying the effort in the downward direction instead of applying it upwards 
when the bucket is lifted up without the use of pulley. 
(d) To obtain gain in speed: when a pair of scissors is used to cut the cloth, its blades move 
longer on cloth while its handles move a little. 
 
 
Question 4: 
What is the purpose of a jack in lifting a car by it? 
 
 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
Solution 4: 
The purpose of jack is to make the effort less than the load so that it works as a force multiplier. 
 
 
Question 5: 
What do you understand by an ideal machine? How does it differ from a practical machine? 
Solution 5: 
An ideal machine is a machine whose parts are weightless and frictionless so that which there is 
no dissipation of energy in any manner. Its efficiency is 100%, i.e. the work output is equal to 
work input. 
 
Ideal machine Practical machine 
1. Efficiency is 100%. 1. Efficiency is less than 100% 
2. Its parts are weightless, elastic 
and perfectly smooth. 
2. Its parts are not weightless, 
elastic or perfectly smooth. 
3. There is no loss in energy due 
to friction. 
3. There is always some loss of 
energy due to friction. 
4. Work output of such a 
machine is equal to the work 
input. 
4. Work output is always less than 
the work input. 
 
 
Question 6: 
Explain the term mechanical advantage. State its unit. 
Solution 6: 
The ratio of the load to the effort is called mechanical advantage of the machine. It has no unit. 
 
 
Question 7: 
Define the term velocity ratio, state its unit. 
Solution 7: 
The ratio of the velocity of effort to the velocity of the load is called the velocity ratio of machine. 
It has no unit. 
 
 
Question 8: 
How is mechanical advantage related to the velocity ratio for an ideal machine? 
Solution 8: 
For an ideal machine mechanical advantage is numerically equal to the velocity ratio. 
Page 3


Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE- 3 (A) 
 
Question 1: 
What do you understand by a simple machine? 
Solution 1: 
A machine is a device by which we can either overcome a large resistive force at some point by 
applying a small force at a convenient point and in a desired direction or by which we can obtain 
a gain in the speed. 
 
 
Question 2: 
State four ways in which machines are useful to us? 
Solution 2: 
Machines are useful to us in the following ways: 
(1) In lifting a heavy load by applying a less effort. 
(2) In changing the point of application of effort to a convenient point. 
(3) In changing the direction of effort to a convenient direction. 
(4) For obtaining a gain in speed. 
 
 
Question 3: 
Name a machine for each of the following use: 
(a) to multiply force 
(b) To change the point of application of force 
(c) To change the direction of force 
(d) To obtain gain in speed 
Solution 3: 
(a) To multiply force: a jack is used to lift a car. 
(b) To change the point of application of force: the wheel of a cycle is rotated with the help of a 
chain by applying the force on the pedal. 
(c) To change the direction of force: a single fixed pulley is used to lift a bucket full of water 
from the well by applying the effort in the downward direction instead of applying it upwards 
when the bucket is lifted up without the use of pulley. 
(d) To obtain gain in speed: when a pair of scissors is used to cut the cloth, its blades move 
longer on cloth while its handles move a little. 
 
 
Question 4: 
What is the purpose of a jack in lifting a car by it? 
 
 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
Solution 4: 
The purpose of jack is to make the effort less than the load so that it works as a force multiplier. 
 
 
Question 5: 
What do you understand by an ideal machine? How does it differ from a practical machine? 
Solution 5: 
An ideal machine is a machine whose parts are weightless and frictionless so that which there is 
no dissipation of energy in any manner. Its efficiency is 100%, i.e. the work output is equal to 
work input. 
 
Ideal machine Practical machine 
1. Efficiency is 100%. 1. Efficiency is less than 100% 
2. Its parts are weightless, elastic 
and perfectly smooth. 
2. Its parts are not weightless, 
elastic or perfectly smooth. 
3. There is no loss in energy due 
to friction. 
3. There is always some loss of 
energy due to friction. 
4. Work output of such a 
machine is equal to the work 
input. 
4. Work output is always less than 
the work input. 
 
 
Question 6: 
Explain the term mechanical advantage. State its unit. 
Solution 6: 
The ratio of the load to the effort is called mechanical advantage of the machine. It has no unit. 
 
 
Question 7: 
Define the term velocity ratio, state its unit. 
Solution 7: 
The ratio of the velocity of effort to the velocity of the load is called the velocity ratio of machine. 
It has no unit. 
 
 
Question 8: 
How is mechanical advantage related to the velocity ratio for an ideal machine? 
Solution 8: 
For an ideal machine mechanical advantage is numerically equal to the velocity ratio. 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
 
Question 9: 
Define the term efficiency of a machine. Why is a machine not 100% efficient?  
Solution 9: 
It is the ratio of the useful work done by the machine to the work put into the machine by the 
effort. 
In actual machine there is always some loss of energy due to friction and weight of moving parts, 
thus the output energy is always less than the input energy. 
 
 
Question 10: 
When does a machine act as (a) a force multiplier (b) a speed multiplier Can a machine act as a 
force multiplier and a speed multiplier simultaneously? 
Solution 10: 
(a) A machine acts as a force multiplier when the effort arm is longer than the load arm. The 
mechanical advantage of such machines is greater than 1. 
(b) A machine acts a speed multiplier when the effort arm is shorter than the load arm. The 
mechanical advantage of such machines is less than 1. 
 
It is not possible for a machine to act as a force multiplier and speed multiplier simultaneously. 
This is because machines which are force multipliers cannot gain in speed and vice-versa. 
 
 
Question 11: 
State the relationship between mechanical advantage, velocity ratio and efficiency. Name the 
term that will not change for a machine of a given design. 
Solution 11: 
Mechanical advantage is equal to the product of velocity ratio and efficiency. 
M.A = ? × V.R 
For a machine of a given design, the velocity ratio does not change. 
 
 
Question 12: 
Derive the relationship between mechanical advantage, velocity ratio and efficiency of a 
machine. 
Solution 12: 
Let a machine overcome a load L by the application of an effort E. In time t, let the displacement 
of effort be dE and the displacement of load be dL. 
Work input = Effort X displacement of effort 
= E X dE 
Work output = Load X displacement of load 
= L X dL 
Page 4


Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE- 3 (A) 
 
Question 1: 
What do you understand by a simple machine? 
Solution 1: 
A machine is a device by which we can either overcome a large resistive force at some point by 
applying a small force at a convenient point and in a desired direction or by which we can obtain 
a gain in the speed. 
 
 
Question 2: 
State four ways in which machines are useful to us? 
Solution 2: 
Machines are useful to us in the following ways: 
(1) In lifting a heavy load by applying a less effort. 
(2) In changing the point of application of effort to a convenient point. 
(3) In changing the direction of effort to a convenient direction. 
(4) For obtaining a gain in speed. 
 
 
Question 3: 
Name a machine for each of the following use: 
(a) to multiply force 
(b) To change the point of application of force 
(c) To change the direction of force 
(d) To obtain gain in speed 
Solution 3: 
(a) To multiply force: a jack is used to lift a car. 
(b) To change the point of application of force: the wheel of a cycle is rotated with the help of a 
chain by applying the force on the pedal. 
(c) To change the direction of force: a single fixed pulley is used to lift a bucket full of water 
from the well by applying the effort in the downward direction instead of applying it upwards 
when the bucket is lifted up without the use of pulley. 
(d) To obtain gain in speed: when a pair of scissors is used to cut the cloth, its blades move 
longer on cloth while its handles move a little. 
 
 
Question 4: 
What is the purpose of a jack in lifting a car by it? 
 
 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
Solution 4: 
The purpose of jack is to make the effort less than the load so that it works as a force multiplier. 
 
 
Question 5: 
What do you understand by an ideal machine? How does it differ from a practical machine? 
Solution 5: 
An ideal machine is a machine whose parts are weightless and frictionless so that which there is 
no dissipation of energy in any manner. Its efficiency is 100%, i.e. the work output is equal to 
work input. 
 
Ideal machine Practical machine 
1. Efficiency is 100%. 1. Efficiency is less than 100% 
2. Its parts are weightless, elastic 
and perfectly smooth. 
2. Its parts are not weightless, 
elastic or perfectly smooth. 
3. There is no loss in energy due 
to friction. 
3. There is always some loss of 
energy due to friction. 
4. Work output of such a 
machine is equal to the work 
input. 
4. Work output is always less than 
the work input. 
 
 
Question 6: 
Explain the term mechanical advantage. State its unit. 
Solution 6: 
The ratio of the load to the effort is called mechanical advantage of the machine. It has no unit. 
 
 
Question 7: 
Define the term velocity ratio, state its unit. 
Solution 7: 
The ratio of the velocity of effort to the velocity of the load is called the velocity ratio of machine. 
It has no unit. 
 
 
Question 8: 
How is mechanical advantage related to the velocity ratio for an ideal machine? 
Solution 8: 
For an ideal machine mechanical advantage is numerically equal to the velocity ratio. 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
 
Question 9: 
Define the term efficiency of a machine. Why is a machine not 100% efficient?  
Solution 9: 
It is the ratio of the useful work done by the machine to the work put into the machine by the 
effort. 
In actual machine there is always some loss of energy due to friction and weight of moving parts, 
thus the output energy is always less than the input energy. 
 
 
Question 10: 
When does a machine act as (a) a force multiplier (b) a speed multiplier Can a machine act as a 
force multiplier and a speed multiplier simultaneously? 
Solution 10: 
(a) A machine acts as a force multiplier when the effort arm is longer than the load arm. The 
mechanical advantage of such machines is greater than 1. 
(b) A machine acts a speed multiplier when the effort arm is shorter than the load arm. The 
mechanical advantage of such machines is less than 1. 
 
It is not possible for a machine to act as a force multiplier and speed multiplier simultaneously. 
This is because machines which are force multipliers cannot gain in speed and vice-versa. 
 
 
Question 11: 
State the relationship between mechanical advantage, velocity ratio and efficiency. Name the 
term that will not change for a machine of a given design. 
Solution 11: 
Mechanical advantage is equal to the product of velocity ratio and efficiency. 
M.A = ? × V.R 
For a machine of a given design, the velocity ratio does not change. 
 
 
Question 12: 
Derive the relationship between mechanical advantage, velocity ratio and efficiency of a 
machine. 
Solution 12: 
Let a machine overcome a load L by the application of an effort E. In time t, let the displacement 
of effort be dE and the displacement of load be dL. 
Work input = Effort X displacement of effort 
= E X dE 
Work output = Load X displacement of load 
= L X dL 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
Efficiency ?? = 
???????? ???????????? ???????? ?????????? 
?? = 
?? ×?? ?? ?? × ?? ?? = 
?? ?? × 
1
?? ?? ?? ?? /
 
But 
?? ?? = ?? . ?? 
?? ?? ?? ?? = ?? . ?? 
?? = 
?? .?? ?? .?? 
M.A = n × V.R 
Thus, mechanical advantage of a machine is equal to the product of its efficiency and velocity 
ratio. 
 
 
Question 13: 
How is the mechanical advantage related with the velocity ratio for an actual machine? State 
whether the efficiency of such a machine is equal to 1, less than 1 or more than 1. 
Solution 13: 
The mechanical advantage for an actual machine is equal to the product of its efficiency and 
velocity ratio. 
M.A = V.R × n 
The efficiency of such a machine is always less than 1, i.e. h<1. This is because there is always 
some loss in energy in form of friction etc. 
 
 
Question 14: 
State reason why is mechanical advantage less than the velocity ratio for an actual machine. 
Solution 14: 
This is because the output work is always less than the input work, so the efficiency is always 
less than 1 because of energy loss due to friction. 
M.A = V.R × n 
 
 
Question 15: 
What is a lever? State its principle. 
Solution 15: 
A lever is a rigid, straight or bent bar which is capable of turning about a fixed axis. 
Principle: A lever works on the principle of moments. For an ideal lever, it is assumed that the 
lever is weightless and frictionless. In the equilibrium position of the lever, by the principle of 
moments, 
Moment of load about the fulcrum=Moment of the effort about the fulcrum. 
 
Page 5


Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
                      
 
EXERCISE- 3 (A) 
 
Question 1: 
What do you understand by a simple machine? 
Solution 1: 
A machine is a device by which we can either overcome a large resistive force at some point by 
applying a small force at a convenient point and in a desired direction or by which we can obtain 
a gain in the speed. 
 
 
Question 2: 
State four ways in which machines are useful to us? 
Solution 2: 
Machines are useful to us in the following ways: 
(1) In lifting a heavy load by applying a less effort. 
(2) In changing the point of application of effort to a convenient point. 
(3) In changing the direction of effort to a convenient direction. 
(4) For obtaining a gain in speed. 
 
 
Question 3: 
Name a machine for each of the following use: 
(a) to multiply force 
(b) To change the point of application of force 
(c) To change the direction of force 
(d) To obtain gain in speed 
Solution 3: 
(a) To multiply force: a jack is used to lift a car. 
(b) To change the point of application of force: the wheel of a cycle is rotated with the help of a 
chain by applying the force on the pedal. 
(c) To change the direction of force: a single fixed pulley is used to lift a bucket full of water 
from the well by applying the effort in the downward direction instead of applying it upwards 
when the bucket is lifted up without the use of pulley. 
(d) To obtain gain in speed: when a pair of scissors is used to cut the cloth, its blades move 
longer on cloth while its handles move a little. 
 
 
Question 4: 
What is the purpose of a jack in lifting a car by it? 
 
 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
Solution 4: 
The purpose of jack is to make the effort less than the load so that it works as a force multiplier. 
 
 
Question 5: 
What do you understand by an ideal machine? How does it differ from a practical machine? 
Solution 5: 
An ideal machine is a machine whose parts are weightless and frictionless so that which there is 
no dissipation of energy in any manner. Its efficiency is 100%, i.e. the work output is equal to 
work input. 
 
Ideal machine Practical machine 
1. Efficiency is 100%. 1. Efficiency is less than 100% 
2. Its parts are weightless, elastic 
and perfectly smooth. 
2. Its parts are not weightless, 
elastic or perfectly smooth. 
3. There is no loss in energy due 
to friction. 
3. There is always some loss of 
energy due to friction. 
4. Work output of such a 
machine is equal to the work 
input. 
4. Work output is always less than 
the work input. 
 
 
Question 6: 
Explain the term mechanical advantage. State its unit. 
Solution 6: 
The ratio of the load to the effort is called mechanical advantage of the machine. It has no unit. 
 
 
Question 7: 
Define the term velocity ratio, state its unit. 
Solution 7: 
The ratio of the velocity of effort to the velocity of the load is called the velocity ratio of machine. 
It has no unit. 
 
 
Question 8: 
How is mechanical advantage related to the velocity ratio for an ideal machine? 
Solution 8: 
For an ideal machine mechanical advantage is numerically equal to the velocity ratio. 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
 
Question 9: 
Define the term efficiency of a machine. Why is a machine not 100% efficient?  
Solution 9: 
It is the ratio of the useful work done by the machine to the work put into the machine by the 
effort. 
In actual machine there is always some loss of energy due to friction and weight of moving parts, 
thus the output energy is always less than the input energy. 
 
 
Question 10: 
When does a machine act as (a) a force multiplier (b) a speed multiplier Can a machine act as a 
force multiplier and a speed multiplier simultaneously? 
Solution 10: 
(a) A machine acts as a force multiplier when the effort arm is longer than the load arm. The 
mechanical advantage of such machines is greater than 1. 
(b) A machine acts a speed multiplier when the effort arm is shorter than the load arm. The 
mechanical advantage of such machines is less than 1. 
 
It is not possible for a machine to act as a force multiplier and speed multiplier simultaneously. 
This is because machines which are force multipliers cannot gain in speed and vice-versa. 
 
 
Question 11: 
State the relationship between mechanical advantage, velocity ratio and efficiency. Name the 
term that will not change for a machine of a given design. 
Solution 11: 
Mechanical advantage is equal to the product of velocity ratio and efficiency. 
M.A = ? × V.R 
For a machine of a given design, the velocity ratio does not change. 
 
 
Question 12: 
Derive the relationship between mechanical advantage, velocity ratio and efficiency of a 
machine. 
Solution 12: 
Let a machine overcome a load L by the application of an effort E. In time t, let the displacement 
of effort be dE and the displacement of load be dL. 
Work input = Effort X displacement of effort 
= E X dE 
Work output = Load X displacement of load 
= L X dL 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
Efficiency ?? = 
???????? ???????????? ???????? ?????????? 
?? = 
?? ×?? ?? ?? × ?? ?? = 
?? ?? × 
1
?? ?? ?? ?? /
 
But 
?? ?? = ?? . ?? 
?? ?? ?? ?? = ?? . ?? 
?? = 
?? .?? ?? .?? 
M.A = n × V.R 
Thus, mechanical advantage of a machine is equal to the product of its efficiency and velocity 
ratio. 
 
 
Question 13: 
How is the mechanical advantage related with the velocity ratio for an actual machine? State 
whether the efficiency of such a machine is equal to 1, less than 1 or more than 1. 
Solution 13: 
The mechanical advantage for an actual machine is equal to the product of its efficiency and 
velocity ratio. 
M.A = V.R × n 
The efficiency of such a machine is always less than 1, i.e. h<1. This is because there is always 
some loss in energy in form of friction etc. 
 
 
Question 14: 
State reason why is mechanical advantage less than the velocity ratio for an actual machine. 
Solution 14: 
This is because the output work is always less than the input work, so the efficiency is always 
less than 1 because of energy loss due to friction. 
M.A = V.R × n 
 
 
Question 15: 
What is a lever? State its principle. 
Solution 15: 
A lever is a rigid, straight or bent bar which is capable of turning about a fixed axis. 
Principle: A lever works on the principle of moments. For an ideal lever, it is assumed that the 
lever is weightless and frictionless. In the equilibrium position of the lever, by the principle of 
moments, 
Moment of load about the fulcrum=Moment of the effort about the fulcrum. 
 
Class X Chapter 3 – Machines  Physics 
_____________________________________________________________________________ 
 
 
Question 16: 
Write down a relation expressing the mechanical advantage of a lever. 
Solution 16: 
M.A = 
Effortarm
Loadarm
 
This is the expression of the mechanical advantage of a lever. 
 
 
Question 17: 
Name the three classes of levers and distinguish between them. Give two examples of each class. 
Solution 17: 
The three classes of levers are: 
(i) Class I levers: In these types of levers, the fulcrum F is in between the effort E and the load 
L. Example: a seesaw, a pair of scissors, crowbar. 
(ii) Class II levers: In these types of levers, the load L is in between the effort E and the fulcrum 
F. The effort arm is thus always longer than the load arm. Example: a nut cracker, a bottle 
opener. 
(iii) Class III levers: In these types of levers, the effort E is in between the fulcrum F and the 
load L and the effort arm is always smaller than the load arm. Example: sugar tongs, 
forearm used for lifting a load. 
 
 
Question 18: 
Give one example each of a class I lever where mechanical advantage is (a) more than one, and 
(b) less than one. 
What is the use of the lever if its mechanical advantage is less than I? 
Solution 18: 
(a) More than one: shears used for cutting the thin metal sheets. 
(b) Less than one: a pair of scissors whose blades are longer than its handles. 
 
When the mechanical advantage is less than 1, the levers are used to obtain gain in speed. This 
implies that the displacement of load is more as compared to the displacement of effort. 
 
 
Question 19: 
A pair of scissors and a pair of pliers both belongs to the same class of levers. Name the class of 
lever. Which one has the mechanical advantage less than 1? 
Solution 19: 
A pair of scissors and a pair of pliers both belong to class I lever. 
A pair of scissors has mechanical advantage less than 1.