##### VMC VIQ Scholarship Test

ApplyRegister for Vidyamandir Intellect Quest. Get Scholarship and Cash Rewards.

Edited By Safeer PP | Updated on Sep 01, 2022 04:33 PM IST

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.

This Story also Contains

- NCERT Exemplar Class 9 Science Solutions Chapter 9-MCQ
- NCERT Exemplar Class 9 Science Solutions Chapter 9-Short Answer Type
- NCERT Exemplar Class 9 Science Solutions Chapter 9-Long Answer Type
- Important Topics of NCERT Exemplar Solutions Class 9 Science Chapter 9:
- NCERT Class 9 Science Exemplar Solutions for Other Chapters:
- Features of NCERT Exemplar Class 9 Science Solutions Chapter 9:

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.Velocity is a vector quantity, which has direction and magnitude.

Magnitude of velocity is called speed, and if speed is changing that means velocity is also changing.

Therefore, for any object moving on a straight line with acceleration will have changing speed or velocity.

By Newton’s second law, acceleration is the effect caused by force hence force must be acting on the body.

For going away from Earth, the net force on the body must be more than Mg. The force must be in vertically upward direction also.

Hence by using the given information, we can say that the body needs not to go away from Earth.

Hence, the correct option is C

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.The force of action and reaction will have same magnitude.

The force of action and reaction will have opposite directions.

The force of action and reaction acts on different bodies.

For example if body A applies force on body B of magnitude 5 N towards the right, then body B will apply force on body A of magnitude 5 N towards the left.

Hence, the correct option is option B

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.Correct option is b.

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.For bodies with more inertia required more force to change its velocity. We can say that inertia is the property which resists change in motion.

Physically inertia can be seen as a mass of the body.

Correct option of this question is C.

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.Hence the correct answer is option a

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.We know that friction always opposes the motion and tries to reduce the speed. In presence of friction, an external agent has to apply an equal force in opposite direction to maintain the speed.

As in this question, there is no friction on the floor, the external agent need not apply any force.

The correct answer is option B.

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.Mass of the rocket is not conserved, the energy of the rocket is not conserved and velocity of the rocket is not conserved.

Hence, the correct answer is option C.

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.This property of inertia, causes water to move forward on the sudden application of break.

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.Physically this property of inertia can be seen as the mass of the body. Hence the property of inertia will be more if Mass is more.

As the three objects taken in this question, have the same size and shape, it means their volume is equal. We know that mass of any body is equal to the product of density and volume. Therefore, we can claim that the object with maximum density will have maximum mass and thus maximum inertia. Therefore, steel will have maximum inertia.

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.As the floor is frictionless both the balls will maintain their speed. Therefore, we can say both the balls will be moving at the same speed.

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.We know, force is the change in momentum in unit time. Hence, we can say that the lighter gun will apply more force: as the same momentum is changed 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.So in the above example, the momentum has the same magnitude but its direction is totally reversed in the journey.

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/sQuestion:15

Answer:

By Newton’s second law, we know that force on a body is equal to the product of mass and acceleration.F = ma

Therefore acceleration can be calculated as the ratio of force and mass,

a =F/m

Now in this question force is halved and mass of the truck is doubled.

Therefore, the new acceleration will be one-fourth of the original.

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.Therefore, in this Phenomenon: both the friends will move in the opposite direction.

This motion will cause: increase in separation between them.

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 10^{3} 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.Now as the moving bullet with the speed 10

By using the third equation of motion: we can find out the acceleration as we know the initial velocity, final velocity and displacement.

Hence the force will be:

By the first equation of motion:

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.F = ma

If a force is applied on 1kg block and it can produce an acceleration of 1 m/s

We can find out the mass of both bodies by using the above equation:

When they are combined,

total mass will be:

Now the acceleration will be:

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:

If a body of mass m is moving with velocity v, its momentum is defined as product of mass and velocity.

P = mv

The unit of momentum is kg m/s.

The direction of momentum will be the same as the direction of velocity.

Suppose a body of mass 1 kg is moving with 5m/s towards the north and another body of same mass is moving towards the south with the same velocity.

Their momentum will not be the same as they have a different direction.

The force is defined as the rate of change in momentum. If force is not applied on the body. its momentum will be conserved.

1

2nd graph: If velocity is fixed, momentum increases linearly with mass. The graph will be a straight line passing through the origin.

NCERT exemplar Class 9 Science solutions chapter 9 explores the below-mentioned topics:

- Mathematical cause and effect relation of force and acceleration.
- Three laws of motion.
- NCERT Exemplar Class 9 science solutions chapter 9 by various examples, explains the identification of action and reaction pair which follows newton’s third law.
- By this chapter, we understand that force is required to change the state of rest or motion which is depicted in Newton’s first law.

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 |

1. Q1. If a ball is kept on a floor and earth attracts it with the force W, then what will be the reaction force?

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.

2. Q2. What is inertia in physics?

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.

3. Q3. “If somebody slaps any person, by the law of action and reaction, another person also applies the same force”. Who hits whom in this case?

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.

4. Q4. If earth attracts different bodies by different forces, why do all of them fall with the same acceleration under gravity?

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

5. Q5. Will there be a long answer question from this chapter in the final examination?

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.

Sep 17, 2024

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

Get answers from students and experts

Register for Vidyamandir Intellect Quest. Get Scholarship and Cash Rewards.

Register for Tallentex '25 - One of The Biggest Talent Encouragement Exam

As per latest 2024 syllabus. Physics formulas, equations, & laws of class 11 & 12th chapters

As per latest 2024 syllabus. Chemistry formulas, equations, & laws of class 11 & 12th chapters

Accepted by more than 11,000 universities in over 150 countries worldwide

Register now for PTE & Unlock 20% OFF : Use promo code: 'C360SPL20'. Limited Period Offer! Trusted by 3,500+ universities globally

News and Notifications

Back to top