# Laws of Motion Exe-3D Short Answer Physics Class-9 ICSE Selina Publishers

Laws of Motion Exe-3D Newton’s Third Law Short Answer Type for Class-9 ICSE Concise Physics. There is the solutions of short Answer type Questions of your latest textbook which is applicable in 2023-24 academic sessionVisit official Website CISCE for detail information about ICSE Board Class-9.

## Laws of Motion Exe-3D Newton’s Third Law Short Answer

(ICSE Class – 9 Physics Concise Selina Publishers)

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

### Exe-3D Newton’s Third Law Short Answer Type

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

Page 81

#### Question 1. State the Usefulness of Newton’s third law of motion.

Newton’s third law explains how a force acts on an object.

#### Question 2. State and explain the law of action and reaction. by giving twoexamples.

Law of action and reaction: In an interaction of two bodies A and B, the magnitude of action, i.e. the force FAB applied by the body B on the body A, is equal in magnitude to the reaction, i.e., the force FBA applied by the body A on the body B, but they are in directions opposite to each other.

##### Examples of Law of action and reaction

(i) When a book is placed on a table, it does not move downwards. It implies that the resultant force on the book is zero, which is possible only if the table exerts an upward force of reaction on the book, equal to the weight of the book.

(ii) While moving on the ground, we exert a force by our feet to push the ground backwards; the ground exerts a force of the same magnitude on our feet forward, which makes it easier for us to move.

Explanation of Law of action and reaction

In the above stated example, there are two objects and two forces. the first example, the weight of the book acts downwards (action) and the force of the table acts upwards (reaction).

while In the second example, our feet exerts a force on the ground (action) and the ground exerts an equal and opposite force (reaction) on our feet.

#### Question 3. Explain the motion of a rocket with the help of Newton’s third law.

When a rocket moves in space, it pushes gases outside, i.e. the rocket applies force on the gases in the backward direction. As a reaction, the gases put equal amount of force on the rocket in the opposite direction and the rocket moves in the forward direction.

#### Question 4. When a shot is fired from a gun, the gun is recoiled. Explain.

When a man fires a bullet from a gun, a force F is exerted on the bullet (action), and the gun experiences an equal and opposite recoil (reaction) and hence gets recoiled

#### Question 5. When you step ashore from a stationary boat, it tends to leave the shore. Explain.

When a man exerts a force (action) on the boat by stepping into it, its force of reaction makes him step out of the boat, and the boat tends to leave the shore due to the force exerted by the man (i.e. action).

#### Question 6. When two spring balances joined at their free ends are pulled apart, both show the same reading. Explain.

Couple two spring balances A and B as shown in the figure. When we pull the balance B, both the balances show the same reading indicating that both the action and reaction forces are equal and opposite. In this case, the pull of either of the two spring balances can be regarded as action and that of the other balance as the reaction

(Laws of Motion Exe-3D Short Class-9 ICSE)

#### Question 7. To move a boat ahead in water, the boatman has to push the water backwards by his oar. Explain.

To move a boat, the boatman pushes (action) the water backwards with his oar. In this response, the water exerts an equal and opposite force (reaction) in the forward direction on the boat due to which the boat moves ahead.

#### Question 8. A person pushing a wall hard is liable to fall backwards. Give reason.

A person pushing a wall hard (action) by his palm, experiences a force (reaction) exerted by the wall on his palm in the opposite direction; thus, he is liable to fall backwards.