# Class 9 Physics Chapter 4

Updated: 21 Oct 2023

286

Class 9 Physics Chapter 4 is about “Turning Effect of Forces”. This article includes topics such as Force Diagrams, Like Parallel Forces, Unlike Parallel Forces, Head to Tail Rule, Addition of Forces, Resolution of Forces, Center of Mass, Center of Gravity, Rotational Motion, Rigid objects, Axis of Rotation, Difference between Center of Gravity and Center of Mass, Torque or Moment of Force, Clock and Anti-Clock wise Torque, Couple, Equilibrium, Conditions of equilibrium, First Condition of Equilibrium, Second Condition of Equilibrium, Principle of Moments, Types of Equilibrium, Static Equilibrium, Dynamic Equilibrium, Stability, Stable Equilibrium, Unstable Equilibrium and Neutral Equilibrium.

## Class 9 Physics Chapter 4 Notes

### Turning Effect of Forces Notes

Class 9 Physics Chapter 4 Notes

### Class 9 Physics Chapter 4 SLO Notes

Class 9 Physics Chapter 4 Notes SLO Notes

## Class 9 Physics Chapter 4 MCQs

### Force Diagrams

1 Which of the following diagrams represents the forces acting on an object?
(a) Force diagram
(b) Resultant diagram
(c) Motion diagram
(d) Velocity diagram

Force diagram

### Like Parallel Forces

2 When two forces act in the same direction, they are called:
(a) Like parallel forces
(b) Unlike parallel forces
(c) Anti-parallel forces
(d) All of these

Like parallel forces

### Unlike Parallel Forces

3 When two forces act in opposite directions, they are called:
(a) Like parallel forces
(b) Unlike parallel forces
(c) Anti-parallel forces
(d) All of these

Unlike parallel forces

4 The method of adding forces tip to tail is known as:
(a) Like parallel forces
(c) Force composition

5 Addition of vectors are done by:
(a) Right hand rule
(b) Left hand rule
(d) None of these

6 The sum of all forces acting on an object is known as:
(a) Balanced force
(b) Unbalanced force
(c) Net force
(d) Equilibrium force

Net force

7 Component of vector acting along the x-axis,
(a) Horizontal component
(b) Vertical component
(c) x-component
(d) All of these

Horizontal component

8 Component of vector acting along the y-axis,
(a) Horizontal component
(b) Vertical component
(c) y-component
(d) All of these

Vertical component

9 The process of combining forces to get a single force, is
(a) Resolution of forces
(b) Subtraction of forces
(d) Multiplication of forces

10 When two forces act in the same direction, their magnitudes are 10N and 15N . What is the net force when added together,
(a) 5N
(b) 10N
(c) 15N
(d) 25N

25N

11 When two forces act in the opposite direction, their magnitudes are same. What is the net force when added together?
(a) 0 N
(b) 10N
(c) 20 N
(d) 30 N

0 N

12 A car is being pulled to the right with a force of 500 N and to the left with a force of 300 N. what is the net force acting on the car?
(a) 200 N to the right
(b) 200 N to the left
(c) 500 N to the right
(d) 500 N to the left

200 N to the right

### Resolution of Forces

13 The process of splitting a force vector into its component is,
(b) Component of forces
(c) Resolution of forces
(d) None of these

Resolution of forces

14 The process opposite to addition of forces is,
(a) Combination of forces
(b) Resolution of forces
(c) Net force
(d) All of these

Resolution of forces

15 If the components of a force vector are perpendicular to each other then such components are called,
(a) Parallel components
(b) Perpendicular components
(c) Rectangular components
(d) Tangential component

Rectangular components

16 The horizontal component of force vector F is represented by,
(a) F_x
(b) F_y
(c) F_z
(d) None of these

F_x

17 The vertical component of force vector F is represented by,
(a) F_x
(b) F_y
(c) F_z
(d) None of these

F_y

18 When resolving a force into components, the magnitudes of components are determined using which trigonometric functions?
(a) Sine and cosine
(b) Tangent and secant
(c) Sine and tangent
(d) Cosine and tangent

Sine and cosine

19 A force of 50 N makes an angle of 30 \ degrees with the horizontal axis. What is the magnitude of horizontal component?
(a) 25 N
(b) 30 N
(c) 43.3 N
(d) 48.5 N

43.3 N

20 A force of 50 N makes an angle of 30 degrees with the horizontal axis. What is the magnitude of vertical component?
(a) 25 N
(b) 30 N
(c) 43.3 N
(d) 48.5 N

25 N

21 The direction of resultant force is determined using which trigonometric function?
(a) Sine
(b) Cosine
(c) Tangent
(d) Secant

Tangent

22 The angle at which x and y components of force are equal is
(a) 0^°
(b) 30^°
(c) 45^°
(d) 60^°

45^°

23 Value of sin 45^° ,
(a) 0.56
(b) 0.707
(c) 0
(d) 1

0.707

### Center of Gravity

24 The point of a body about which the mass is equally distributed in all direction, is
(a) Canter of mass
(b) Center of gravity
(c) Axis of rotation
(d) All of these

Canter of mass

25 The point where whole weight of a body appear to act is called,
(a) Canter of mass
(b) Center of gravity
(c) Axis of rotation
(d) All of these

Center of gravity

26 The position of center of gravity depends on ………… of a body.
(a) Size
(b) Weight
(c) Shape
(d) All of these

Shape

27 The center of mass is generally represented by,
(a) CM
(b) CG
(c) MC
(d) GC

CM

28 The center of gravity is generally represented by,
(a) CM
(b) CG
(c) MC
(d) GC

CG

29 The center of gravity of a regular shaped body is always on its center of,
(a) Body
(b) Axis
(c) Symmetry
(d) None of these

Symmetry

30 The acceleration due to gravity ……………. with altitude.
(a) Stay same
(b) Increasing
(c) Decreases
(d) Zero

Decreases

### Rotational Motion

31 The motion of a body about a fix point is said to be,
(a) Circular motion
(b) Vibrational motion
(c) Rotational motion
(d) None of these

Rotational motion

#### Rigid objects

32 The objects that do not deforms when move, are known as
(a) Solid objects
(b) Rigid objects
(c) Strong objects
(d) None of these

Rigid objects

### Moment of Force

33 The rotational effect of a body is measured by a quantity known as:
(a) Acceleration
(b) Velocity
(c) Displacement
(d) Torque

Torque

34 Turning effect produced in a body about fixed point due to applied force is known as,
(a) Acceleration
(b) Torque
(c) Displacement
(d) Velocity

Torque

35 Torque is also known as,
(a) Moment of force
(b) Rotational motion
(c) Force
(d) None of these

Moment of force

36 Torque is a ……… quantity:
(a) Base
(b) Vector
(c) Scalar
(d) All of these

Vector

37 Torque is represented is by,
(a) \tau
(b) t
(c) M
(d) T

\tau

38 The mathematical formula for Torque is,
(a) \tau = F \times d
(b) \tau = ma
(c) \tau = mg
(d) None of these

\tau = F \times d

39 The Moment of force is measured in,
(a) Kg/m^3
(b) Nm
(c) N/m
(d) N/m^2

Nm

40 The rotation produced in a body depends upon ……….. factors
(a) 1
(b) 2
(c) 3
(d) 4

2

41 If the rotation is produced in anti-clock wise direction then the torque is taken as:
(a) Opposite
(b) Perpendicular
(c) Positive
(d) Negative

Positive

42 If the rotation is produced in clock wise direction then the torque is taken as:
(a) Opposite
(b) Perpendicular
(c) Positive
(d) Negative

Negative

43 The point around which a rigid object rotates is called:
(a) Axis of rotation
(b) Center of mass
(c) Rotational pivot
(d) Fixed point

Axis of rotation

44 The perpendicular distance between the axis of rotation and the line of action of the force is called:
(a) Moment arm
(b) Force distance
(c) Torque arm

Moment arm

45 Moment arm is measured in,
(a) Kilogram
(b) Meter
(c) Second
(d) Newton

Meter

46 The force that causes an object to rotate about an axis is known as:
(a) Torque
(b) Moment arm
(c) Rotational force
(d) Centripetal force

Centripetal force

#### Clock wise Torque

47 When a force tends to cause clockwise rotation, it is called:
(a) Anti-clockwise torque
(b) Clockwise torque
(c) Rotational counterforce
(d) Inverse rotational force

Clockwise torque

#### Anti-clock wise Torque

48 When a force tends to cause anti-clockwise rotation, it is called:
(a) Anti-clockwise torque
(b) Clockwise torque
(c) Rotational counterforce
(d) Inverse rotational force

Anti-clockwise torque

### Couple

49 When two equal, opposite and parallel forces act at two points of the same body, they form a:
(a) Torque
(b) Moment arm
(c) Force
(d) Couple

Couple

50 What is the name given to two parallel forces with the same magnitude but opposite directions?
(a) Parallel forces
(b) Disparate forces
(c) Balanced forces
(d) Couple forces

Couple forces

51 The distance between the two forces in a couple is known as:
(a) Torque distance
(b) Couple arm
(c) Moment arm
(d) Rotational distance

Couple arm

52 A ……………. is always acting while opening or closing water tap, a lock, stopper of a bottle or jar:
(a) Couple
(b) Weight
(c) Force
(d) All of these

Couple

### Equilibrium

53 When an object is at rest and the sum of all forces acting on it is zero, it is known as:
(a) Dynamic equilibrium
(b) Static equilibrium
(c) Translational equilibrium
(d) Rotational equilibrium

Static equilibrium

54 The study of objects in equilibrium is called,
(a) Statics
(b) Dynamic
(c) Kinetic
(d) All of these

Statics

### Conditions of equilibrium

55 There are …………… conditions of equilibrium.
(a) 1
(b) 2
(c) 3
(d) 4

2

#### First Condition of Equilibrium

56 The first condition of equilibrium states that an object will remain at rest if:
(a) The net force is zero
(b) The net torque is zero
(c) The net displacement is zero
(d) The net velocity is zero

The net force is zero

57 The first condition of equilibrium is represented by,
(a) \sum F = 0
(b) \sum P = 0
(c) \sum \tau =0
(d) All of these

\sum F = 0

#### Second Condition of Equilibrium

58 The second condition of equilibrium states that an object will remain in equilibrium if:
(a) The net force is zero
(b) The net torque is zero
(c) The net displacement is zero
(d) The net velocity is zero

The net torque is zero

59 The second condition of equilibrium is represented by,
(a) \sum F = 0
(b) \sum P = 0
(c) \sum \tau =0
(d) All of these

\sum \tau =0

60 The symbol \sum used for,
(a) Summation
(b) Multiplication
(c) Division
(d) None of these

Summation

### Principle of Moments

61 The principle that states that for an object to be in equilibrium, the sum of clockwise torques must equal the sum of anticlockwise torques is called:
(a) Equilibrium principle
(b) Principle of Moment
(c) Force balance principle
(d) Torque equilibrium principle

Principle of Moment

### Types of Equilibrium

#### Dynamic Equilibrium

62 When an object is in motion with constant velocity, it is said to be in:
(a) Static equilibrium
(b) Dynamic equilibrium
(c) Stable equilibrium
(d) Unstable equilibrium

Dynamic equilibrium

63 When an object is in motion with uniform linear velocity, it is said to be in:
(a) Static equilibrium
(b) Dynamic translational equilibrium
(c) Dynamic rotational equilibrium
(d) Unstable equilibrium

Dynamic translational equilibrium

64 When an object is in motion with uniform angular velocity, it is said to be in:
(a) Static equilibrium
(b) Dynamic translational equilibrium
(c) Dynamic rotational equilibrium
(d) Unstable equilibrium

Dynamic rotational equilibrium

65 Paratrooper falling down with constant linear velocity is an example of,
(a) Static equilibrium
(b) Dynamic translational equilibrium
(c) Dynamic rotational equilibrium
(d) Unstable equilibrium

Dynamic translational equilibrium

66 A compact disk (CD) rotating with constant angular velocity is an example of,
(a) Static equilibrium
(b) Dynamic translational equilibrium
(c) Dynamic rotational equilibrium
(d) Unstable equilibrium

Dynamic rotational equilibrium

### Stability

67 …………………. is a measure of how hard it is to displace an object from equilibrium.
(a) Stability
(b) Force
(c) Torque
(d) Equilibrium

Stability

#### Neutral Equilibrium

68 An equilibrium position where a small displacement from the position cause a restoring force is called:
(a) Stable equilibrium
(b) Unstable equilibrium
(c) Neutral equilibrium
(d) Dynamic equilibrium

Stable equilibrium

69 An equilibrium position where a small displacement from the position results in an increased displacement is called:
(a) Stable equilibrium
(b) Unstable equilibrium
(c) Neutral equilibrium
(d) Dynamic equilibrium

Unstable equilibrium

70 The total sum of forces acting on an object in static equilibrium is:
(a) Zero
(b) Unpredictable
(c) Constant
(d) Infinite

Zero

71 The total sum of torques acting on an object in rotational equilibrium is:
(a) Zero
(b) Negative
(c) Positive
(d) Variable

Zero

72 In which state of equilibrium the center of gravity raised than the original position.
(a) Stable equilibrium
(b) Unstable equilibrium
(c) Neutral equilibrium
(d) Dynamic equilibrium

Stable equilibrium

73 In which state of equilibrium the center of gravity lowered than the original position.
(a) Stable equilibrium
(b) Unstable equilibrium
(c) Neutral equilibrium
(d) Dynamic equilibrium

Unstable equilibrium

74 In which state of equilibrium the center of gravity remain same as the original position.
(a) Stable equilibrium
(b) Unstable equilibrium
(c) Neutral equilibrium
(d) Dynamic equilibrium

Neutral equilibrium

75 The weight of racing car is kept low to make it,
(a) Stable
(b) Unstable
(c) Strong
(d) None of these

Stable

76 A physics book lying on the table is an example of ……………..
(a) Stable equilibrium
(b) Unstable equilibrium
(c) Neutral equilibrium
(d) Dynamic equilibrium

Stable equilibrium

77 A ball balanced on the tip of narrow cone is an example of……….
(a) Stable equilibrium
(b) Unstable equilibrium
(c) Neutral equilibrium
(d) Dynamic equilibrium

Unstable equilibrium

78 Motion of rolling ball on ground is an example of ………………..
(a) Stable equilibrium
(b) Unstable equilibrium
(c) Neutral equilibrium
(d) Dynamic equilibrium

Neutral equilibrium

79 The stability of a body can be increased by …………….. the area of support.
(a) Increasing
(b) Decreasing
(c) Keeping the same
(d) All of these

Increasing

80 The stability of a body can be increased by …………….. the center of mass.
(a) Raising
(b) Lowering
(c) Accelerating
(d) None of these