# Class 9 Physics Chapter 3

Updated: 19 Oct 2023

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Class 9 Physics Chapter 3 is about Dynamics”. This article includes topics such as Definition of Dynamics, Force, Newton’s Law of Motion, Inertia, Newton’s First Law of Motion, Newton’s Second Law of Motion, Newton’s Third Law of Motion, Mass, Weight, Linear Momentum, Force and Change in Momentum, Isolated System, Change of Momentum and Collison’s, Change of Momentum and Expulsive Forces, Rocket Propulsion and Thrust, Friction, Normal Force, Types of Frictional Forces, Static Friction, Kinetic Friction, Coefficient Friction, Advantages of Friction, Disadvantages of Friction, Rolling Friction, Methods of Reducing Friction, Tension, Uniform Circular Motion, Centripetal Acceleration and Centripetal Force.

## Class 9 Physics Chapter 3 Notes

### Dynamics Notes

Class 9 Physics Chapter 3 Notes

### Class 9 Physics Chapter 3 SLO Notes

Class 9 Physics Chapter 3 SLO Notes

## Class 9 Physics Chapter 3 MCQs

### Dynamics

1 The branch of mechanics which deals with the study of motion by analyzing the cause of motion is called
(a) Kinematics
(b) Dynamics
(c) Optics
(d) Thermodynamics

Dynamics

### Force

2 A push or a pull on an object is called
(a) Work
(b) Energy
(c) Force
(d) Momentum

Force

3 Force is a …………. quantity.
(a) Scalar
(b) Vector
(c) Tensor
(d) None of these

Vector

Vector 4 What is the unit of force in the SI system?
(a) Joule
(b) Pascal
(c) Newton
(d) Watt

Newton

5 What is the symbol of force?
(a) F
(b) M
(c) A
(d) V

F

6 Force is a vector quantity. What does this mean?
(a) It has magnitude only
(b) It has direction only
(c) It has both magnitude and direction
(d) It has neither magnitude nor direction

It has both magnitude and direction

7 How can Newton (N) be expressed in terms of fundamental units?
(a) Nm^2/kg
(b) kg/m^2
(c) kgm/s^2
(d) N/kg

kgm/s^2

8 Which of the following is an example of a contact force?
(a) Gravitational force
(b) Magnetic force
(c) Frictional force
(d) Electric force

Frictional force

9 Which of the following is an example of a non-contact force?
(a) Frictional force
(b) Magnetic force
(c) Normal force
(d) Applied force

Magnetic force

10 In which book did Newton publish his laws of motion?
(a) Physics
(b) Elements
(c) Optics
(d) Philosophiæ Naturalis Principia Mathematica

Philosophiæ Naturalis Principia Mathematica

### Newton’s Law of Motion

11 Law of motion was presented by:
(a) Einstein
(b) Newton
(c) Galileo
(d) None of these

Newton

### Inertia

12 Newton’s first law of motion is also known as the law of:
(a) Acceleration
(b) Force and motion
(c) Inertia
(d) Interaction

Inertia

13 The property of a body due to which it retain its state is called
(a) Inertia
(b) Force
(c) Work
(d) Energy

Inertia

14 A physical quantity which moves or tends to move, stops or tends to stop a moving object is called
(a) Inertia
(b) Force
(c) Momentum
(d) Work

Force

15 The quantitative measure of inertia is called
(a) Force
(b) Inertia
(c) Mass
(d) Time

Mass

16 Law of inertia is actually the …………. Law of motion
(a) 1^{st}
(b) 2^{nd}
(c) 3^{rd}
(d) None of these

1^{st}

17 The SI unit of inertia is
(a) Second
(b) Kilogram
(c) Meter
(d) Ampere

Kilogram

### Newton’s Second Law of Motion

18. The acceleration of an object is directly proportional to force and inversely proportional to the mass, is the statement of
(a) 1^{st} \ law
(b) 2^{nd} \ law
(c) 3^{rd} \ law
(d) None of these

2^{nd} \ law

19 When force is applied on a body, ………………… is produced in the body?
(a) Energy
(b) Force
(c) Acceleration
(d) None of these

Acceleration

20 The formula F=ma represents:
(a) Newton’s first law
(b) Newton’s second law
(c) Newton’s third law
(d) None of these

Newton’s second law

21 The acceleration produced in a body is always in the direction of:
(a) Applied force
(b) Momentum
(c) Mass
(d) Energy

Applied force

22 If the mass of the body is doubled while keeping the force constant then acceleration will be:
(a) Double
(b) Triple
(c) One half
(d) None of these

One half

23 If the force is doubled while keeping the mass constant then acceleration will be:
(a) Double
(b) Triple
(c) One half
(d) None of these

Double

24 What will be the acceleration if applied force is 10 N on an object of mass 5 kg?
(a) 1 m/s^2
(b) 2 m/s^2
(c) 3 m/s^2
(d) 4 m/s^2

2 m/s^2

25 What will be the force produced an acceleration of 3 m/s^2 in an object of mass 5 kg?
(a) 5 N
(b) 10 N
(c) 15 N
(d) 20 N

15 N

### Newton’s Third Law of Motion

26 According to Newton’s third law of motion, if object A exerts a force on object B, the reaction force is:
(a) Zero
(b) Perpendicular to the force on object A
(c) In the opposite direction to the force on object A
(d) In the same direction as the force on object A

In the opposite direction to the force on object A

27 Action and reaction are equal in magnitude but opposite in direction is known as …………. Law of motion.
(a) 1st
(b) 2nd
(c) 3rd
(d) None of these

3rd

28 The mathematical expression for Newton third law is:
(a) F_A= - F_B
(b) F = ma
(c) F_A = F_B
(d) None of these

F_A= - F_B

(a) F_A is parallel to F_B
(b) F_A is perpendicular to F_B
(c) F_A is in opposite direction to F_B
(d) F_A is in same direction to F_B

F_A is in opposite direction to F_B

30 Walking on the road is an example of:
(a) Newton’s first law
(b) Newton’s second law
(c) Newton’s third law
(d) None of these

Newton’s third law

31 Weight is the force experienced by an object due to its:
(a) Mass
(b) volume
(c) density
(d) speed

Mass

### Mass and Weight

#### Weight

32 What is the symbol for weight?
(a) F
(b) M
(c) N
(d) W

W

33 The weight of an object varies from place to place because:
(a) The mass of the object changes
(b) The acceleration due to gravity changes
(c) The object’s volume changes
(d) None of these

The acceleration due to gravity changes

34 What is the unit of weight in the SI system?
(a) Newton
(b) Kilogram
(c) Pound
(d) Watt

Newton

35 Weight is a……………. quantity.
(a) Scalar
(b) Vector
(c) Tensor
(d) All of these

Vector

36 What is the formula for calculating weight (W) of an object?
(a) W = mg
(b) W = mv
(c) W = ma
(d) None of these

W = mg

37 Calculate the weight of an object with a mass of 5 kg (take \ g = 9.81 m/s^2).
(a) 49.05 N
(b) 14.29 N
(c) 45.67 N
(d) 20.21 N

49.05 N

38 The weight of the body of mass 10 kg on earth surface is:
(a) 32 N
(b) 50 N
(c) 98 N
(d) 102 N

98 N

39 The ………….. of the body is always acting towards the center of the earth.
(a) Mass
(b) Weight
(c) Force
(d) All of these

Weight

40 The force with which the object is attracted toward the center of the earth is:
(a) Mass
(b) Electric force
(c) Magnetic force
(d) Weight

Weight

41 The physical quantity that varies from place to place is:
(a) Mass
(b) Weight
(c) Both A and B
(d) None of these

Weight

42 What is the value of acceleration due to gravity (g) on Earth’s surface?
(a) 1.62 m/s^2
(b) 5.33 m/s^2
(c) 24.7 m/s^2
(d) 9.8 m/s^2

9.8 m/s^2

43 What is the value of acceleration due to gravity (g) on the surface of Moon?
(a) 1.62 m/s^2
(b) 5.33 m/s^2
(c) 24.7 m/s^2
(d) 9.8 m/s^2

1.62 m/s^2

#### Mass

44 The amount of matter in an object is called
(a) Weight
(b) Force
(c) Mass
(d) Momentum

Mass

45 What is the symbol for mass?
(a) M
(b) W
(c) F
(d) S

M

46 What is the unit of mass in the SI system?
(a) Newton
(b) Kilogram
(c) Pound
(d) Watt

Kilogram

47 Mass is a ……………. Quantity.
(a) Scalar
(b) Vector
(c) Tensor
(d) All of these

Scalar

48 The physical quantity that remains same everywhere is:
(a) Mass
(b) Weight
(c) Both A and B
(d) None of these

Mass

### Linear Momentum

49 The product of an object’s mass and velocity is called:
(a) Force
(b) Weight
(c) Linear momentum
(d) None of these

Linear momentum

50 The quantity of motion in a body is called
(a) Force
(b) Weight
(c) Linear momentum
(d) None of these

Linear momentum

51 What is the symbol for linear momentum?
(a) L
(b) M
(c) V
(d) P

P

52 What is the unit of linear momentum?
(a) kg m/s
(b) Ns
(c) m/s
(d) Both (a) and (b)

Both (a) and (b)

53 What is the formula for calculating linear momentum (P) of an object?
(a) P = mv
(b) P = ma
(c) P = mg
(d) All of these

P = mv

54 Linear momentum is a ………… quantity.
(a) Scalar
(b) Vector
(c) Tensor
(d) All of these

Vector

55 Calculate the linear momentum of an object with a mass of 2 kg and a velocity of 3 m/s .
(a) 5 kg m/s
(b) 8 kg m/s
(c) 6 kg m/s
(d) 1 kg m/s

6 kg m/s

56 The rate of change in momentum is called
(a) Mass
(b) Weight
(c) Force
(d) Energy

Force

### Isolated System

57 A system with no external forces acting on it is said to be:
(a) Isolated system
(b) Opened system
(c) Closed system
(d) None of these

Isolated system

58 The total momentum of an isolated system is constant, is stated by:
(a) Law of conservation of energy
(b) Law of conservation of mass
(c) Law of conservation of momentum
(d) All of these

Law of conservation of momentum

### Change of Momentum and Collisions

59 An event during which particles come close to each other and interact by means of a force is called
(a) Collision
(b) Explosion
(c) Interaction
(d) None of these

Collision

### Change of Momentum and Expulsive Forces

60 An event during which particles move away from each other after collision is called
(a) Collision
(b) Explosion
(c) Interaction
(d) None of these

Explosion

### Friction

61 The force that opposes motion between two surfaces in contact is called
(a) Weight
(b) Momentum
(c) Friction
(d) Tension

Friction

62 What is the symbol for friction?
(a) f
(b) T
(c) F
(d) g

f

63 What is the unit of friction in the SI system?
(a) Newton
(b) Kilogram
(c) Pascal
(d) Watt

Newton

64 Friction is a …………….. Quantity.
(a) Scalar
(b) Vector
(c) Tensor
(d) None of these

Vector

65 In which direction does friction act when an object moves on a surface?
(a) In the same direction as motion
(b) Opposite to the direction of motion
(c) Perpendicular to the direction of motion
(d) None of these

Opposite to the direction of motion

### Types of Frictional Forces

#### Static Friction

66 Friction experienced by an object at rest:
(a) Static friction
(b) Kinetic friction
(c) Sliding friction
(d) Rolling friction

Static friction

67 The maximum value of static friction is known as
(a) Static friction
(b) Kinetic friction
(c) Limiting friction
(d) Sliding friction

Limiting friction

#### Kinetic Friction

68 Friction experienced by an object in motion:
(a) Static friction
(b) Kinetic friction
(c) Sliding friction
(d) Rolling friction

Kinetic friction

69 Which condition is true?
(a) f_s > f_k
(b) f_s < f_k
(c) f_s = f_k
(d) None of these

f_s > f_k

### Normal Force

70 A contact force perpendicular to the surface of contact objects is:
(a) Friction
(b) Normal force
(c) Tension
(d) Centripetal force

Normal force

71 What is the symbol for normal force:
(a) f
(b) T
(c) FN
(d) All of these

FN

72 What is the unit of normal force in the SI system?
(a) Newton
(b) Kilogram
(c) Pascal
(d) Watt

Newton

73 The ratio of the frictional force to the normal force is:
(a) Tension
(b) Coefficient of friction
(c) Normal force
(d) None of these

Coefficient of friction

### Coefficient Friction

74 What is the unit of coefficient of friction in the SI system?
(a) Newton
(b) Kilogram
(c) Pascal
(d) Dimensionless (no unit)

Dimensionless (no unit)

75 What is the symbol for the coefficient of friction?
(a) C
(b) F
(c) \mu
(d) W

\mu

### Sliding Friction

76 Friction experienced by an object in motion along a surface is:
(a) Sliding friction
(b) Rolling friction
(c) Tension
(d) None of these

Sliding friction

### Rolling Friction

77 Friction experienced by a rolling object is:
(a) Sliding friction
(b) Rolling friction
(c) Tension
(d) None of these

Rolling friction

### Methods of Reducing Friction

78 What is one way to reduce friction between two surfaces in contact?
(a) Increase the normal force between the surfaces
(b) Increase the mass of the objects
(c) Apply a lubricant between the surfaces
(d) None of these

Apply a lubricant between the surfaces

### Tension

79 The force exerted by a rope, string, or cable on an object which is attached with it, is called
(a) Friction
(b) Tension
(c) Normal force
(d) All of these

Tension

80 ……………….. is a pulling force.
(a) Friction
(b) Tension
(c) Normal force
(d) All of these

Tension

81 What is the symbol for tension?
(a) T
(b) N
(c) F
(d) L

T

82 What is the unit of tension in the SI system?
(a) Newton
(b) Kilogram
(c) Pascal
(d) Watt

Newton

83 When is tension taken as positive?
(a) When the rope is being pulled up
(b) When the rope is at rest
(c) When the rope is being pulled down
(d) None of these

When the rope is being pulled up

84 When is tension taken as negative?
(a) When the rope is being pulled up
(b) When the rope is at rest
(c) When the rope is being pulled down
(d) None of these

When the rope is being pulled down

85 A machine consisting of two different masses connected by a string running over a pulley is
(a) Washing machine
(b) Atwood machine
(c) Juicer machine
(d) None of these

Atwood machine

### Uniform Circular Motion

86 Motion at a constant speed along a circular path is:
(a) Uniform circular motion
(b) Non-uniform circular motion
(c) Motion in a straight line
(d) All of these

Uniform circular motion

87 Motion at varying speeds along a circular path is:
(a) Uniform circular motion
(b) Non-uniform circular motion
(c) Motion in a straight line
(d) All of these

Non-uniform circular motion

### Centripetal Acceleration

88 Acceleration directed towards the center of a circle is
(a) Acceleration
(b) Centripetal acceleration
(c) Centrifugal acceleration
(d) Angular acceleration

Centripetal acceleration

89 What is the symbol for centripetal acceleration?
(a) A
(b) c
(c) a_c
(d) A_C

a_c

90 What is the unit of centripetal acceleration in the SI system?
(a) m/s^2
(b) m/s
(c) Ns
(d) kg

m/s^2

91 What is the formula for calculating the magnitude of centripetal acceleration (a_c) of an object moving in a circle of radius (r) at a speed (v) ?
(a) a_c = r/v
(b) a_c = v/r
(c) a_c = v^2/r
(d) a_c = r^2/v

a_c = v^2/r

92 Calculate the magnitude of centripetal acceleration of an object moving in a circle of radius 2 meters at a speed of 3 m/s .
(a) 1 m/s^2
(b) 6 m/s^2
(c) 4.5 m/s^2
(d) 9 m/s^2

4.5 m/s^2

93 Calculate the magnitude of centripetal acceleration of an object moving in a circle of radius 5 meters at a speed of 5 m/s .
(a) 5 m/s^2
(b) 6 m/s^2
(c) 25 m/s^2
(d) 9 m/s^2

5 m/s^2

### Centripetal Force

94 The force that keeps an object moving in a circular path is
(a) Friction
(b) Centripetal force
(c) Centrifugal force
(d) None of these

Centripetal force

95 What is the symbol for centripetal force?
(a) F_c
(b) f
(c) C
(d) L

F_c

96 What is the unit of centripetal force in the SI system?
(a) Newton
(b) Kilogram
(c) Pascal
(d) Watt

Newton

97 What is the formula for calculating magnitude of centripetal force acting on an object moving in a circle of mass (m) at a speed (v) with a radius (r) ?
(a) F_C = mv
(b) F_C = ma
(c) F_C = mv^2/r
(d) F_C = m/r

F_C = mv^2/r

98 Calculate the magnitude of centripetal force acting on an object with a mass of 10 kg moving in a circle of radius 5 \ meters at a speed of 8 m/s .
(a) 200 N
(b) 40 N
(c) 32 N
(d) 128 N

128 N

99 The force that keeps planets in their orbits around the sun is
(a) Friction
(b) Centripetal force
(c) Centrifugal force
(d) None of these

Centripetal force

100 The force that pulls an object away from the center of a circle is
(a) Friction
(b) Centripetal force
(c) Centrifugal force
(d) None of these