CBSE Class 9 Science NCERT Solutions: Chapter 9, Force and Laws of Motion
However hard you work on a topic, you cannot succeed until you practice the same. To help students get enough practice, NCERT books offer a variety of questions at the end of each chapter. These can be short or long answer type questions, multiple choice type questions or fill-in-the-blanks questions. Students must try to get appropriate answers to all these questions as it will help to get a thorough understanding of each topic and gain confidence to solve other related problems in the examinations.
Thus, in order to score optimum marks in the board papers, it is very important for the students to practice a variety of questions.
To help students find the right approach to all the NCERT questions, we are providing detailed and accurate solutions. These solutions will help you know the right explanation for each NCERT question and understand the technique to write perfect answers in the annual examinations.
In this article we are providing NCERT Solutions for Class 9 Science Chapter 9 - Force and Laws of Motion. All these solutions have been prepared by the subject matter experts and will help you clear your concepts. Students may download the NCERT solutions for Class 9 Science chapter - Force and Laws of Motion, in PDF format.
Main topics discussed in Class 9 Science chapter- Force and Laws of Motion are:
- Balanced and unbalanced forces
- First law of motion
- Inertia and mass
- Second law of motion
- Mathematical formulation of second law of motion
- Third law of motion
- Cconservation of momentum.
Some of the questions and their solutions from NCERT Solutions for Class 9: Force and Laws of Motion, are as follows:
Q. Which of the following has more inertia?
(a) A rubber ball and a stone of the same size?
(b) A bicycle and a train?
(c) A five-rupee coin and a one-rupee coin?
Inertia of an object is the measurement of its mass.
(a) A stone of same size as that of rubber ball will have a greater mass because the stone will have more inertia.
(b) A train has much greater mass than that of a bicycle, so the train will have more inertia.
(c) A five-rupee coin has more mass than a one-rupee coin, so five-rupee coin will have greater inertia.
Q. Explain why some of the leaves may get detached from a tree if we vigorously shake its branch?
We know that the leaves are attached to the tree and are in a state of rest initially. But when the tree is vigorously shaken, the branches of the tree comes in the state of motion but the leaves tend to maintain their state of rest, as a result the leaves get detached from the tree and fall down.
Q. If action is always equal to the reaction, explain how a horse can pull a cart?
In order to pull the cart horse pushes the ground with its foot in the backward direction by pressing the ground. As a reaction of this force, the ground pushes the horse in forward direction. As a result the cart is pulled by the horse in the forward direction.
Q. An object experiences a net zero external unbalanced force. Is it possible for the object to be travelling with a non-zero velocity? If yes, state the conditions that must be placed on the magnitude and direction of the velocity. If no, provide a reason.
According to the Newton's 1st law of motion, no net force is required to move an object which is moving with a constant velocity. So, when an object experiences a net zero external unbalanced force, then it can move with a non-zero velocity. Also, if an object is initially at rest not net force acts upon it, thus the object may not move at all.
Q. Why is it "advised to tie any luggage kept on the roof of a bus with a rope?
It is advised to tie any luggage kept on the roof of a bus because when the bus stops suddenly, it readily comes in the state of rest but the luggage remains in the state of motion. So, due to inertia of motion, the luggage will move forward and would fall down from the roof of the bus. If the bus starts suddenly, then bus comes in the state of motion but luggage remains in the state of rest. Due to inertia of rest, the luggage moves in the backward direction and will fall down.
Q. According to the third law of motion, when we push on an object, the object pushes back on us with an equal and opposite force. If the object is a massive truck parked along the roadside, it will probably not move. A student justifies this by answering that the two opposite and equal forces cancel each other. Comment on this logic and explain why the truck does not move.
The logic given by the student is not correct because two equal and opposite forces cancel each other only in the case if they act on the same body. According to Newton’s third law, action and reaction force always act on two different bodies, so they cannot cancel each other. When a massive truck is pushed, then the truck may not move because the force applied is not sufficient to move the truck.
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