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NCERT exemplar Class 9 Science solutions chapter 9 involves the learning and understanding of three laws of Newton. The applications of Newton's laws and numerical problems are discussed in the chapter. These NCERT exemplar Class 9 Science chapter 9 solutions are prepared by the subject matter experts with more than 10+ years of experience. Students can enhance and test their learnings of this chapter through NCERT exemplar Class 9 Science chapter 9 solutions. These NCERT exemplar Class 9 Science solutions chapter 9 develop a better understanding of three laws of motion. CBSE Class 9 Syllabus is rigidly followed while creating these solutions.
Question:1
Which of the following statement is not correct for an object moving along a straight path in an accelerated motion?
(a) Its speed keeps changing
(b) Its velocity always changes
(c) It always goes away from the earth
(d) A force is always acting on it
Answer:c
By the knowledge of kinematics, we can say that acceleration changes velocity of any moving object.Question:2
According to the third law of motion, action and reaction
(a) always act on the same body
(b) always act on different bodies in opposite directions
(c) have same magnitude and directions
(d) act on either body at normal to each other
Answer:
According to Newton’s third law, every action has an equal and opposite reaction.Question:3
A goalkeeper in a game of football pulls his hands backwards after holding the ball shot at the goal. This enables the goal keeper to:
(a) exert larger force on the ball
(b) reduce the force exerted by the ball on hands
(c) increase the rate of change of momentum
(d) decrease the rate of change of momentum
Answer:b
We know that force is equal to the rate of change of momentum. When a moving ball is caught by the goalkeeper, ultimately it stops. It means the change in momentum of the ball will be same whether he catches the ball directly or by moving his hands backwards. By moving his hand backwards during the catch, he gives more time to change the momentum of the ball. This process ensures minimum acceleration, hence the force will be minimum by the goalkeeper on the ball. The law of action-reaction says that the force on the goalkeeper by the ball will also be minimum.Question:4
The inertia of an object tends to cause the object
(a) to increase its speed
(b) to decrease its speed
(c) to resist any change in its state of motion
(d) to decelerate due to friction
Answer:c
As defined in Newton’s first law, everybody has the property of inertia.| This property of inertia of the body tries to maintain the state of rest or motion with constant velocity. The property of inertia opposes the change in the state of rest or uniform motion. A force is required to change the state of rest or uniform motion.Question:5
A passenger in a moving train tosses a coin which falls behind him. It means that motion of the train is
(a) accelerated
(b) uniform
(c) retarded
(d) along circular tracks
Answer:a
Sol. When a body is detached from any other body, it acquires the same velocity as the original body. That means, when the passenger tosses the coin, the initial horizontal speed of coin is equal to the speed of passenger sitting in the train. If the train would be moving with constant speed then the coin falls at a point directly below the line of motion, just like as we throw it on ground. If train will be accelerated, the passenger will travel more distance forward and he will find that the coin will fall backward. If train will be decelerated then passenger will travel less distance forward and he will find that coin will fall forward.Question:6
An object of mass 2 kg is sliding with a constant velocity of 4 ms–1 on a frictionless horizontal table. The force required to keep the object moving with the same velocity is
(a) 32 N
(b) 0 N
(c) 2 N
(d) 8 N
Answer:b
If the object moving with some speed on the frictionless ground, then there is no force which will try to reduce its speed.Question:7
Rocket works on the principle of conservation of
(a) mass
(b) energy
(c) momentum
(d) velocity
Answer:c
For the motion of the rocket, hot gases get exhausted from the rocket and they apply thrust force on the rocket. If we consider rocket and the gases as a single body, then to conserve momentum: gases are pushed backwards and the rocket will be pushed forward. Suppose, you are sitting in a toy car and you jump in forwarding direction, the car will go backwards to conserve momentum. The same phenomena happen with rocket and exhausted gases.Question:8
A water tanker filled up to 2/3 of its height is moving with a uniform speed. On sudden application of the brake, the water in the tank would
(a) move backward
(b) move forward
(c) be unaffected
(d) rise upwards
Answer:b
When the tank is moving forward, the water in the tank is also moving forward with the same speed. If suddenly brakes are applied, the tank decreases its speed but water cannot decrease its speed immediately because of its inertia. Hence it seems to travel more distance in forward direction in comparison with the tank.The correct answer to this question is option b.
Question:9
Answer:
By Newton’s first law, we understand that everybody has the property of inertia. Inertia opposes the change in the state of rest or uniform motion.Question:10
Answer:
When two balls are kept on the floor of the train, both of them are moving with the speed of the train. When brakes are applied, the train stopped suddenly but the speed of balls remain the same as there is no force acting on balls. Therefore, these balls seem to move forward in the train.Question:11
Answer:
In both cases: the bullet is fired with the same force, therefore the momentum of the bullet will be the same in both cases. By conservation of momentum, we can say the momentum of both the guns would be the same. As momentum is the same for both the guns, the velocity of the lighter gun will be more. Therefore, a lighter gun will strike the shoulder in lesser time.Question:12
A horse continues to apply a force in order to move a cart with a constant speed. Explain why?
Answer:
The horse constantly applies force on the cart to maintain the speed of the cart. It seems that only force on the cart is applied by horse, so its speed must be increasing. But, as the cart is moving on the road, a friction force from the road must be acting opposite to the direction of motion. The force by horse overcome the force applied by friction. If the horse would not apply any force, the cart will slow down.Question:13
Answer:
When we throw a ball upwards with some speed, it’s its speed decreases because the acceleration of gravity acts downward. It goes up to a height till its velocity becomes zero. Force of gravity still acts in the downward direction, which increases the speed in the downward direction. When the ball reaches the same level, it acquires the same speed but in opposite direction. We know that momentum is a vector quantity, which has the same direction as of velocity.Question:14
Answer:
If we observe the graph, the speed of the ball decreases from 80 m/s to 0 m/s in 8 seconds. We know that acceleration is the rate of change of velocity. It can be calculated as the ratio of change in velocity and time. Therefore, the acceleration will be 10 m/s2. This acceleration is caused by the force of friction. By Newton’s second law, we know that F = Ma. Mass of the ball is 50 g which will be equal to 0.05 kg. By putting the value of mass and acceleration, we will get that the friction force will be equal to 0.5 N.Question:15
Answer:
By Newton’s second law, we know that force on a body is equal to the product of mass and acceleration.Question:16
Answer:
As the first friend throws the ball away from him, he will be pushed backwards. This occurs due to the conservation of linear momentum principle. Now when the second front catches the ball, he moves in the direction of motion of the ball. This also occurs, due to conservation of momentum principle.Question:17
Answer:
When water comes out from the sprinkler, it applies the opposite force on the sprinkler. This can be understood: by the principle of momentum conservation or Newton’s third law. The opposite force on the sprinkler, makes it rotate in the opposite sense. We know, by Newton’s third law, the force applied by the sprinkler on the water will cause equal and opposite force on the sprinkler by the water.Question:18
Using second law of motion, derive the relation between force and acceleration. A bullet of 10 g strikes a sand-bag at a speed of 103 ms-1 and gets embedded after travelling 5 cm. Calculate
(i) the resistive force exerted by the sand on the bullet
(ii) the time taken by the bullet to come to rest.
Answer:
By Newton’s second law, we know that force on a body will be equal to the product of mass and acceleration.Question:19
Answer:
By Newton’s second law, we know that force on a body will be equal to the product of mass and acceleration.Question:20
What is momentum? Write its SI unit. Interpret force in terms of momentum. Represent the following graphically
(a) momentum versus velocity when mass is fixed.
(b) momentum versus mass when velocity is constant.
Answer:
NCERT exemplar Class 9 Science solutions chapter 9 explores the below-mentioned topics:
Chapter wise solutions |
Understanding of Class 9 Science NCERT exemplar chapter 9 solutions will be very useful in higher classes and help us to crack various problems of competitive exams like JEE Main and NEET.
Students of Class 9 can leverage these solutions as supplementary study and practice material to get an enhanced understanding of the force and laws of motion-based practice questions.
Due to a wide variety of question base, The NCERT exemplar Class 9 Science solutions chapter 9 are sufficient to attempt other books such as Physics Question Bank by Oswaal Publications, NCERT Class 9 Science textbook, Lakhmir Singh and Manjit Kaur by S. Chand etcetera.
NCERT exemplar Class 9 Science solutions chapter 9 pdf download enables the students to download and refer to these solutions in a pdf format while studying NCERT exemplar Class 9 Science chapter 9 in the offline environment.
Also read - NCERT Solutions for Class 9
Chapter No. | Chapter Name |
Chapter 1 | Matter in Our Surroundings |
Chapter 2 | Is Matter Around Us Pure |
Chapter 3 | Atoms and Molecules |
Chapter 4 | Structure of The Atom |
Chapter 5 | The Fundamental Unit of Life |
Chapter 6 | Tissues |
Chapter 7 | Diversity in Living Organisms |
Chapter 8 | Motion |
Chapter 9 | Force and Laws of Motion |
Chapter 10 | Gravitation |
Chapter 11 | Work and Energy |
Chapter 12 | Sound |
Chapter 13 | Why Do We Fall ill? |
Chapter 14 | Natural Resources |
Chapter 15 | Improvement in Food Resources |
A1. The reaction force will be half the same magnitude W and it is applied by the ball on the earth. Sometimes students mistakenly assume that the normal reaction on the ball is the reaction force but that is not a reaction force.
A2. Inertia is the property of any body which shows opposition in change of state of rest or motion. Mathematically this property of inertia is calculated as mass.
Therefore, we can say that the mass of a body is the inertia of the body.
A3. Undoubtedly both have applied equal and opposite force on each other. However, the sensitivity of the part of the body where the force is applied is different for different organs.
One person is getting force on the cheek and another on the hand. This different sensitivity causes different feelings. If someone slaps on the iron rod then the man who slapped will be hurt.
A4. By Newton's second law, acceleration is the ratio of force and mass, and force by gravity is proportional to mass.
Therefore, acceleration due to gravity is independent of mass
A5. Most certainly, students can expect a long answer from this crucial chapter of Class 9 which can include a definition, derivation, and numerical in a single question. NCERT exemplar Class 9 Science solutions chapter 9 equips the student with the approach to attempt all varieties of problems pertaining to Force and Laws of Motion.
Application Date:09 September,2024 - 14 November,2024
Application Date:09 September,2024 - 14 November,2024
Admit Card Date:13 September,2024 - 07 October,2024
Admit Card Date:13 September,2024 - 07 October,2024
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