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# NCERT Solutions for Class 9 Science Chapter 9 – Force And Laws Of Motion

NCERT Solutions for Class 9 Science Chapter 9 Force and Laws of Motion introduce you to different fundamentals of physics and physical forces like inertia, velocity, the law of conservation of momentum and magnitude of the force. There are concepts about negative and positive signs of forces, their applications and different situations where forces work explained in class 9 NCERT solutions for class 9 science chapter 9.

Class 9 NCERT Science Chapter 9 Force and Laws of Motion contains 3 exercises and 25 questions altogether. The chapter discusses Newton’s laws of motions with its mathematical equations which are used in the chapter to solve numerical problems. Studying the laws of motion might be tricky for you in the beginning as it is a completely new concept. But, if you will solve the NCERT exercises for the topic, it will become easier for you to grasp the concepts.

Use our NCERT solutions for class 9 science chapter 9 whenever you get stuck in any concept of the chapter. We have prepared detailed solutions for you so will be able to understand the topic on your own as you will read them. We have also ensured that the solutions are prepared as per CBSE syllabus so you can rely on them for exam preparation as well.

## Important Topics of NCERT Solutions for Class 9 Science Chapter 9 Force and Laws of Motion

Inertia

CBSE Class 9 Science NCERT Solutions for Class 9 Science Chapter 9 talks about Inertia, which is basically the measure of the mass of a particular body. It is directly proportional to the mass of the body. This means that greater the mass of the body, greater will be the inertia and lesser the mass of the body, lesser will be its inertia.

For example, we can consider a bicycle and a bus. In case of a bus, its mass is much more than that of a bicycle and therefore it has much more inertia as compared to the inertia of a bicycle.

The chapter also deals with the state of motion and rest, in terms of Inertia of the body. Due to the inherent inertia of a body, it tends to stay in its position of motion or of rest.

For example, if a moving bus suddenly stops we tend to fall in a forward direction. This is because in a moving bus the passenger tends to move with the bus, but when the bus stops the body tries to maintain its state of motion and falls forward.

Similarly, when the bus accelerates, we tend to fall backwards, it is because our body is at rest along with the rest position of the bus, when the bus starts our body tries to maintain its inertia of rest and therefore falls back when it accelerates.

Newton’s Laws of Motion

The three laws of motion, given by Newton that are discussed in the chapter. These three laws state that-

1. A body, if moving with a constant velocity and in a straight line, will continue to be in its state of rest or motion until an external force is applied on it.
2. The rate of change of momentum of a body is equal to both, the magnitude and the direction of the force.
3. Every action has an opposite and equal reaction.

Numerical problems

The chapter has numerical questions based on the laws of motion, acceleration, momentum etc.

Example –

Two objects of different masses 100g and 200g are recorded to be moving along the same line and the same direction with their velocities of 2 m/s and 1 m/s respectively. Ultimately they collide and after that, the first object moves at a velocity of 1.67 m/s. Find out the velocity of the second object.

Solution –

Mass of one of the objects, m1 = 100 g = 0.1 kg

Mass of another object, m2 = 200 g = 0.2 kg

Velocity of m1 before the collision, v1 = 2 m/s

Velocity of m2 before collision, v2 = 1 m/s

Velocity of m1 after collision, v3 = 1.67 m/s

Velocity of m2 after collision = v4

According to the law of conservation of momentum:

Total momentum before collision = Total momentum after collision

Therefore m1v1 + m2v2 = m3v3 + m4v4

Therefore v4 = 1.165 m/s

Answer = the velocity of the second object will be 1.165 m/s after the collision took place.

### Exercise-wise discussion of NCERT Class 9 Solutions for Chapter 9 – Force and Laws of Motion

1. Science NCERT Class 9 Chapter 9 – Force and Laws of Motion has a variety of exercises which aim at ensuring that your concepts are well tested and ready to be applied in a problem-solving format.
2. The exercises in the starting of the chapter majorly cover reasoning questions.
3. There are questions which ask you to explain the magnitude of inertia based on different objects and questions which require you to explain the reason behind inertia of rest and motion.
4. There are questions which require elaborations to daily life situations on the basis of Newton’s laws of motion.
5. Further, the exercises cover numerical questions based on the velocity, magnitude, mass, distance and equations of laws of motion.
6. There are reasoning questions which are again based on everyday scenarios.
7. All together the exercises cover all the essential portions of the chapter and the ideas and concepts introduced in it.

### About NCERT Solutions for Class 9 Chapter 9 by Instasolv

• In our NCERT Solutions for Class 9 Chapter 2, we have ensured that the solutions are presented in a stepwise manner so that you learn the fundamental and logic applied behind every answer.
• We have ensured that all your doubts are carefully tackled and you do not struggle in finding various sources to clear them.
• Our solutions are based on all the latest CBSE syllabus for class 9 science.
• We have not left a single question from the chapter; you will have everything required for your exam preparation in the solutions formulated by our experts.

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