# 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

Download Chapter 2 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

## Show Answer

**
Dynamics
**

### Force

2 A push or a pull on an object is called(a) Work

(b) Energy

(c) Force

(d) Momentum

## Show Answer

**
Force
**

3 Force is a …………. quantity.

(a) Scalar

(b) Vector

(c) Tensor

(d) None of these

## Show Answer

**
Vector
**

Vector 4 What is the unit of force in the SI system?

(a) Joule

(b) Pascal

(c) Newton

(d) Watt

## Show Answer

**
Newton
**

5 What is the symbol of force?

(a) F

(b) M

(c) A

(d) V

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
Magnetic force
**

10 In which book did Newton publish his laws of motion?

(a) Physics

(b) Elements

(c) Optics

(d) Philosophiæ Naturalis Principia Mathematica

## Show Answer

**
Philosophiæ Naturalis Principia Mathematica
**

**To Download Complete Notes of Physics Notes 9 Class, Click on the given link.**

### Newton’s Law of Motion

11 Law of motion was presented by:(a) Einstein

(b) Newton

(c) Galileo

(d) None of these

## Show Answer

**
Newton
**

### Newton’s First Law of Motion

### 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

## Show Answer

**
Inertia
**

13 The property of a body due to which it retain its state is called

(a) Inertia

(b) Force

(c) Work

(d) Energy

## Show Answer

**
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

## Show Answer

**
Force
**

15 The quantitative measure of inertia is called

(a) Force

(b) Inertia

(c) Mass

(d) Time

## Show Answer

**
Mass
**

16 Law of inertia is actually the …………. Law of motion

(a) 1^{st}

(b) 2^{nd}

(c) 3^{rd}

(d) None of these

## Show Answer

**
1^{st}
**

17 The SI unit of inertia is

(a) Second

(b) Kilogram

(c) Meter

(d) Ampere

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
F_A= - F_B
**

29 The negative sign in Newton third law of motion indicates:

(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

## Show Answer

**
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

## Show Answer

**
Newton’s third law
**

31 Weight is the force experienced by an object due to its:

(a) Mass

(b) volume

(c) density

(d) speed

## Show Answer

**
Mass
**

### Mass and Weight

#### Weight

32 What is the symbol for weight?(a) F

(b) M

(c) N

(d) W

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
Newton
**

35 Weight is a……………. quantity.

(a) Scalar

(b) Vector

(c) Tensor

(d) All of these

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
1.62 m/s^2
**

#### Mass

44 The amount of matter in an object is called(a) Weight

(b) Force

(c) Mass

(d) Momentum

## Show Answer

**
Mass
**

45 What is the symbol for mass?

(a) M

(b) W

(c) F

(d) S

## Show Answer

**
M
**

46 What is the unit of mass in the SI system?

(a) Newton

(b) Kilogram

(c) Pound

(d) Watt

## Show Answer

**
Kilogram
**

47 Mass is a ……………. Quantity.

(a) Scalar

(b) Vector

(c) Tensor

(d) All of these

## Show Answer

**
Scalar
**

48 The physical quantity that remains same everywhere is:

(a) Mass

(b) Weight

(c) Both A and B

(d) None of these

## Show Answer

**
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

## Show Answer

**
Linear momentum
**

50 The quantity of motion in a body is called

(a) Force

(b) Weight

(c) Linear momentum

(d) None of these

## Show Answer

**
Linear momentum
**

51 What is the symbol for linear momentum?

(a) L

(b) M

(c) V

(d) P

## Show Answer

**
P
**

52 What is the unit of linear momentum?

(a) kg m/s

(b) Ns

(c) m/s

(d) Both (a) and (b)

## Show Answer

**
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

## Show Answer

**
P = mv
**

54 Linear momentum is a ………… quantity.

(a) Scalar

(b) Vector

(c) Tensor

(d) All of these

## Show Answer

**
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

## Show Answer

**
6 kg m/s
**

56 The rate of change in momentum is called

(a) Mass

(b) Weight

(c) Force

(d) Energy

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
Explosion
**

### Friction

61 The force that opposes motion between two surfaces in contact is called(a) Weight

(b) Momentum

(c) Friction

(d) Tension

## Show Answer

**
Friction
**

62 What is the symbol for friction?

(a) f

(b) T

(c) F

(d) g

## Show Answer

**
f
**

63 What is the unit of friction in the SI system?

(a) Newton

(b) Kilogram

(c) Pascal

(d) Watt

## Show Answer

**
Newton
**

64 Friction is a …………….. Quantity.

(a) Scalar

(b) Vector

(c) Tensor

(d) None of these

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
Static friction
**

67 The maximum value of static friction is known as

(a) Static friction

(b) Kinetic friction

(c) Limiting friction

(d) Sliding friction

## Show Answer

**
Limiting friction
**

#### Kinetic Friction

68 Friction experienced by an object in motion:(a) Static friction

(b) Kinetic friction

(c) Sliding friction

(d) Rolling friction

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
Normal force
**

71 What is the symbol for normal force:

(a) f

(b) T

(c) FN

(d) All of these

## Show Answer

**
FN
**

72 What is the unit of normal force in the SI system?

(a) Newton

(b) Kilogram

(c) Pascal

(d) Watt

## Show Answer

**
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

## Show Answer

**
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)

## Show Answer

**
Dimensionless (no unit)
**

75 What is the symbol for the coefficient of friction?

(a) C

(b) F

(c) \mu

(d) W

## Show Answer

**
\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

## Show Answer

**
Sliding friction
**

### Rolling Friction

77 Friction experienced by a rolling object is:(a) Sliding friction

(b) Rolling friction

(c) Tension

(d) None of these

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
Tension
**

80 ……………….. is a pulling force.

(a) Friction

(b) Tension

(c) Normal force

(d) All of these

## Show Answer

**
Tension
**

81 What is the symbol for tension?

(a) T

(b) N

(c) F

(d) L

## Show Answer

**
T
**

82 What is the unit of tension in the SI system?

(a) Newton

(b) Kilogram

(c) Pascal

(d) Watt

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
Centripetal acceleration
**

89 What is the symbol for centripetal acceleration?

(a) A

(b) c

(c) a_c

(d) A_C

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
Centripetal force
**

95 What is the symbol for centripetal force?

(a) F_c

(b) f

(c) C

(d) L

## Show Answer

**
F_c
**

96 What is the unit of centripetal force in the SI system?

(a) Newton

(b) Kilogram

(c) Pascal

(d) Watt

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
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

## Show Answer

**
Centrifugal force
**

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