Machines ICSE Class-10 Concise Selina Physics Solutions Chapter-3. We Provide Step by Step Answer of Exercise-3(A), MCQs-3(A), Numericals-3(A), Exercise-3(B), MCQ-3(B), and Numericals -3(B) Questions of Exercise-3 Machines  ICSE Class-10 . Visit official Website CISCE for detail information about ICSE Board Class-10.

 Board ICSE Publications Selina Publication Subject Physics Class 10th Chapter-3 Machines Book Name Concise Topics Solution of Exercise-3(A), MCQs-3(A), Numericals-3(A), Exercise-3(B), MCQ-3(B), and Numericals -3(B) Academic Session 2021-2022

### Machines ICSE Class-10 Concise Selina Physics Solutions Chapter-3

-: Select Exercise :-

Exercise-3(A), MCQs-3(A), Numericals-3(A),

Exercise-3(B), MCQ-3(B), and Numericals -3(B)

### Important Topics of Chapter-3 Machines for ICSE Class-10

Concept of machine including load, fulcrum and effort.Today is various type machine discuss in Solution of Selina Physics but complex machines are combination of simple machine. Although there are many term in machine yet velocity ratio and efficiency are most important term among machine  . There are many simple machine in Chapter -3 of Selina Physics such that liver.pulley, inclined plane but  in ICSE Physics 2021 only liver and pulley is in latest syllabus.

### Excercise 3 (A) Machines (Selina Concise Physics Solutions)

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#### Question 1

(a) What do you understand by a simple machine?

(b) State the principle of an ideal machine.

(a) 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.

(b) 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.

#### Question 2

State four ways in which machines are useful to us?

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  (Machines ICSE Class-10 Concise )

Name the machine for each of the following use:

(a) to multiply the force,

(b) to change the point of application of force,

(c) to change the direction of force,

(d) to obtain the gain in speed.

(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?

The purpose of jack is to make the effort less than the load so that it works as a force multiplier.

#### Question 5  (Machines ICSE Class-10 Concise )

What do you understand by an ideal machine? How does it differ from a practical machine?

An ideal machine is a machine whose parts are weightless and friction less 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.

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.

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 (i) an ideal machine, (ii) a practical machine?

For an ideal machine mechanical advantage is numerically equal to the velocity ratio.

#### Question 9

Define the term efficiency of a machine. Give two reasons for a machine not to be 100% efficient?

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 and

(b) a speed multiplier? Can a machine act as a force multiplier and speed multiplier simultaneously?

(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

A machine works as a (i) force multiplier, (ii) speed multiplier. In each case state whether the velocity ratio is more than or less than 1.

(i) For a machine working as a force multiplier, displacement of load is less than displacement of effort. Thus, the velocity ratio is more than 1.

(ii) For a machine working as a speed multiplier, displacement of load is more than displacement of effort. Thus, the velocity ratio is less than 1.

#### Question 12  (Machines ICSE Class-10 Concise )

(a) State the relationship between mechanical advantage, velocity ratio and efficiency.

(b) Name the term that will not change for a machine of a given design.

Mechanical advantage is equal to the product of velocity ratio and efficiency.

For a machine of a given design, the velocity ratio does not change.

#### Question 13

Derive the relationship between mechanical advantage, velocity ratio and efficiency of a machine.

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.

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