Laws of Motion Exe-3B Long Answer Physics Class-9 ICSE Selina Publishers

Laws of Motion Exe-3B Newton’s First Law Inertia Long Answer Type for Class-9 ICSE Concise Physics. There is the solutions of Long Answer type Questions of your latest textbook which is applicable in 2023-24 academic session. Visit official Website CISCE for detail information about ICSE Board Class-9.

Laws of Motion Exe-3B Newton’s First Law Inertia Long Answer

(ICSE Class – 9 Physics Concise Selina Publishers)

Board	ICSE
Class	9
Subject	Physics
Writer / Publication	Concise selina Publishers
Chapter-3	Laws of Motion
Exe – 3B	Newton’s First Law Inertia
Topics	Solution of Exe-3(B) Long Answer Type
Academic Session	2023-2024

Exe-3B Newton’s First Law Inertia Long Answer Type

Ch-3 Laws of Motion Physics Class-9 ICSE Concise

Page 70

Question 1. State and explain the law of inertia (or Newton’s first law of motion).

Answer :

Statement of Newton’s first law: If a body is in a state of rest, it will remain in the state of rest, and if the body is in the state of motion, it will remain moving in the same direction with the same speed unless an external force is applied on it.

Explanation: Newton’s first law can be explained in the following two parts:

(i) Definition of inertia:

The 1^st part of Newton’s first law of motion gives the definition of inertia, according to which an object cannot change its state by itself.

Example: A book lying on a table will remain in its position unless it is displaced.

(ii) Definition of force:

The 2^nd part of Newton’s first law defines force, according to which force is that external cause which can move a stationary object or which can stop a moving object.

Example: A book lying on a table is displaced from its place when it is pushed

(Laws of Motion Exe-3B Long Class-9 ICSE)

Question 2. Explain the following:

(a) When a train suddenly moves forward, the passenger standing in the compartment tends to fall backwards.

(b) When a corridor train suddenly starts, the sliding doors of some compartments may open.

(c) After alighting from a moving bus, one has to run for some distance in the direction of bus in order to avoid falling.

(d) Dust particles are removed from a carpet by beating it.

(e) It is advantageous to run before taking a long jump.

Answer:

(a) train suddenly moves forward, the passenger standing in the compartment tends to fall backwards. because

When a train suddenly starts, the passengers tend to fall backwards. This is because the lower part of the body, which is in contact with the train, begins to move while the upper part of the body tends to maintain its position of rest. As a result, the upper part tends to fall backwards.

(b) train suddenly starts, the sliding doors of some compartments may open because

The frame of the sliding door being in contact with the floor of the train also comes in motion on start of the train, but the sliding door remains in its position due to inertia. Thus, the frame moves ahead with the train, while the door slides opposite to the direction of motion of the train. Thus, the door may shut or open accordingly.

(c) alighting from a moving bus, one has to run for some distance because

When people alight from a moving bus, they continue to run alongside the bus to avoid falling. If they were to stop at once, the feet would come to rest suddenly but the upper part of the body would still be in motion and they would tend to fall forward.

(d) Dust particles are removed from a carpet by beating it because

The part of the carpet where the stick strikes comes in motion at once, while the dust particles settled on it remain in the state of rest due to inertia of rest. Thus, a part of the carpet moves ahead with the stick leaving behind the dust particles that fall down due to gravity.