9th Class Physics Chapter 4 Short Questions with Answers Solved

Question: 1

What is centre of gravity.

Answer: 1

1-123

A point where the whole weight of the body appears to act vertically downward is called centre of gravity of a body e.g. centre of gravity of uniform rod is centre of the rod.

Question: 2

Define parallel forces.

Answer: 2

2-123

When a number of forces acting on a body in such a way that their point of action s are different but line of action are parallel to each other ,are called parallel forces.

Question: 3

Differentiate between torque and couple.

Answer: 3

3-123

Torque is produced by only only force one moment arm is there to produce the torque

Question: 4

Differentiate between like and unlike forces.

Answer: 4

4-123

Like parallel forces: such a parallel forces whoe direction is same are called like parallel force. Example: the weights of apples in a sack are parallel to each other and also in the same direction.

Question: 5

Explain 1st condition of equilibrium.

Answer: 5

5-123

A body said to satisfy first condition of equilibrium if the resultant of all these forces acting on it is zero.

Question: 6

Define Resultant vector.

Answer: 6

6-123

A resultant vector is a single vector that has the same effect as the combined effect of all vectors to be added.

Question: 7

Give an example of a moving body which is in equilibrium.

Answer: 7

7-123

WA paratrooper coming down with the constant speed is in equilibrium as well as in motion.

Question: 8

When a body is said to be in equilibrium?

Answer: 8

8-123

A body is said to be in equilibrium if no net force acts on it.

Question: 9

Unit of torque.

Answer: 9

9-123

It unit newton metre.

Question: 10

What is 2nd condition for equilibrium?

Answer: 10

10-123

A body is said to be satisfy 2nd condition of equilibrium if the resultant torque acting on a body is zero.

Question: 11

Write the types of parallel force.

Answer: 11

11-123

i) Like parallel forces. ii) Unlike parallel forces.

Question: 12

Define centre of mass

Answer: 12

12-123

Centre of mass of a system is a point where an applied force causes the system to move without rotation.

Question: 13

Define Trigonometric ratio.

Answer: 13

13-123

The ratios between any two sides of a right angle triangle are called trigonometric ratio.

Question: 14

What is meant by principle of moments?

Answer: 14

14-123

A body is balanced if the sum of clockwise moments acting on the body is equal to the sum of anticlockwise moments acting on its.

Question: 15

Differentiate between stable and neutral equilibrium.

Answer: 15

15-123

Stable equilibrium: A body is said to be in stable equilibrium if after a slight tilt it returns to its previous position

In stable equilibrium centre of gravity of the body is at its lowest position and after the slight tilt it return to its previous position.

Question: 16

What is line of action of force.

Answer: 16

16-123

A line along which a force acts is called line of action of the force.

Question: 17

Can a small child play with a fat child on the sea-saw Explain how

Answer: 17

17-123

Yes a small child can play with a fat child if the fat child sists near the axis of rotation of the sea-saw and the small child sists away the axist of rotation.

Question: 18

Define equilibrium. and give one example.

Answer: 18

18-123

A body is said to be in equilibrium, if no net force acts on it. Example: i) A book lying on a table is in equilibrium because the weight of book and force of reaction of table are in opposite direction and hence cancel their effect.

Question: 19

Which factor torque depends.

Answer: 19

19-123

Torque = F X L So, Torque depends upon force and moment arm.

Question: 20

Give an example of a moving body which is in equilibrium

Answer: 20

20-123

A paratrooper coming down with the constant speed is in equilibrium as well as in motion

Question: 21

Define like parallel forces.

Answer: 21

21-123

Such parallel forces which have same direction are called like parallel forces.

Question: 22

Define moment arm.

Answer: 22

22-123

The perpendicular distance between the axis of rotation and line of action of force is called moment arm.

Question: 23

What is directional graph

Answer: 23

23-123

To draw a vector on a paper we need direction Graphically two mutually perpendicular lines are used to indicate the direction. These two line are used to direct a vector on paper or plane.

Question: 24

Define couple arm.

Answer: 24

24-123

The perpendicular distance between two forces of couple is called couple arm.

Question: 25

Define unlike parallel forces.

Answer: 25

25-123

Such parallel forces which are opposite in direction are called unlike parallel forces.

Question: 26

Define unstable equilibrium. Give one example

Answer: 26

26-123

Unstable equilibrium: If a body does not return to its previous position when set free after a slightest is said to be in unstable equilibrium. Example: A pencil just balanced at its tip with centre of gravity at the highest position is the example of unstable equilibrium=brium

Question: 27

Define torque

Answer: 27

27-123

Turning effect of a force is called torque or moment of force

Question: 28

Define couple with the help of an example.

Answer: 28

28-123

Couple: A couple is formed by two unlike parallel forces same magnitude but not along the same line.

Question: 29

Define parallel forces

Answer: 29

29-123

When a number of forces acting on a body in such a way that their point of actions are different but lines of action are parallel to each other are called parallel forces.

Question: 30

Define Trigonometry.

Answer: 30

30-123

The branch of geometry which explains the properties of right angle triangle is called trigonometry.

Question: 31

Define stable equilibrium with example.

Answer: 31

31-123

Stable equilibrium: A body is said to be in stable equilibrium if after a slightest it returns to its previous position. Example: If a book returns to its previous position after a slightest tilt then book is said be in stable equilibrium.

Question: 32

Differentiate between like and unlike forces

Answer: 32

32-123

Like Parallel forces: Such a parallel forces whose direction is same called are called like parallel forces

Example: The weights of apples in a sack are parallet to each other and also in the same direction.

Question: 33

What is stat of neutral equilibrium.

Answer: 33

33-123

Neutral Equilibrium; If a body remains in its new position when disturbed from its previous position, then body is said to be in neutral equilibrium.

Question: 34

How can we increase the stability of a vehicle

Answer: 34

34-123

Stability of the vehicle can be increased by lowering the centre of mass of vehicle and by making them heavy at the bottom.

Question: 35

Define rigid body and give an example.

Answer: 35

35-123

Rigid body is composed of large number of particles. If the distance between all pairs of particles of the body do not change by applying a force, then it is called a rigid body. Example: Adoor , a cylinder.

Question: 36

What is centre of gravity

Answer: 36

36-123

Centre of Gravity: A point where whole weight of the body appears to act vertically downward is called centre of gravity of a body e.g centre of gravity of uniform rod is centre of the rod

Question: 37

Define Resolution of vectors.

Answer: 37

37-123

Resolution of Vectors: to split up a force into its perpendicular components is called resolution of forces.

Question: 38

Define axis of rotation.

Answer: 38

38-123

The line about which a body rotates is called axis of rotation.

Question: 39

Define Resultant Vector

Answer: 39

39-123

A resultant vector is a single vector that has the same effect as the combined effect of all vector to be added

Question: 40

Why a body cannot be in equilibrium due to single force acting on it

Answer: 40

40-123

When a single force acts on a body acceleration and torque is produced due to this reason a body is not equilibrium.

Question: 41

How head to tail rule helps to find the resultant of forces

Answer: 41

41-123

When two forces are added with head to tail rule it gives the resultant of two forces, It gives the magnitude and direction both of the resultant force.

Question: 42

Why the handle of a door is placed at the outer edge of the door

Answer: 42

42-123

We can open or close door more easily by applying a force at the outer edge of a door rather than near the hinge (axist ) Because by this a long moment arm is obtained which produce more torque which helps to open the door more easily.

Question: 43

Why there is need for 2nd condition of equilibrium if body satisfy 1st condition of equilibrium

Answer: 43

43-123

If a body satisfied 1st condition of equilibrium then it is not completely in equilibrium. Because there is a chance of producing torque in that body

If two same force are acting on a body in opposite direction in a same line then no rotation is produced but if those two forces act in different lines then the torque is produced so we need another condition for equilibrium to eliminate the torques.

Question: 44

In a right angled triangle length of base is 4cm and its perpendicular is 3cm.

Answer: 44

44-123

length of its hypotenuse, cos , sin, tan,

Question: 45

What is 2nd condition for equilibrium

Answer: 45

45-123

A body is said to be satisfy 2nd condition of equilibrium if the resultant torque acting on a body is zero

Question: 46

Define stable equilibrium with example

Answer: 46

46-123

Stable Equilibrium: A body is said to be in stable equilibrium if after a slightest tilt it returns to its previous postion.

Question: 47

How a force can be resolved into its prependicular components

Answer: 47

47-123

To resolve a force into its perpendicular components we neend head to tail rule. It the given forces is considered as resultant force then the two components can be drawn In the figure force F is making an angle 0 with horizontal surface and it is resolved into Fx and Fy which are horizontal and vertical components respectively.

Question: 48

Why the height of a vehicle is kept as low as possible

Answer: 48

48-123

To lower the centre of mass of vehicles their height is kept low. Low centre of mass make them more stable as compare to the high centre of mass Due to this vehicles are made heavy at the bottom and their height is kept minimum

Question: 49

Explain 1st condition for equilibrium.

Answer: 49

49-123

A body is said satisfy first condition of equilibrium if the resultant of all these forces acting on it is zero.

F=0

Question: 50

Think of a body which is at test but not in equilibrium

Answer: 50

50-123

When we throw a body in up ward direction at its highest position the body is at rest for a moment but it is not in equilibrium because no other force is present to cancel the force of weight.

Question: 51

Define like parallel forces

Answer: 51

51-123

Such parallel forces which have same direction are called like parallel forces. e.g in the above figure f1 and f2 are like parallel to each other and the weight of apples closed in a sack are also in downward direction. These forces are also parallel forces.

Question: 52

When a body is said to be in equilibrium

Answer: 52

52-123

A body is said to be in equilibrium if no net force acts on it.

Question: 53

Two children are sitting on the sea-saw such that they cannot swing

Answer: 53

53-123

In this situation the net torque is zero

Question: 54

What is meant by principle of moments

Answer: 54

54-123

A body is balance if the sum of clockwise moments acting on the body is equal to the sum of anticlock wise moments acting on its

Question: 55

What is head to tail rule

Answer: 55

55-123

When two or more than two vectors are added such that the head of the first vector is joined with tail of second vector and finally the tail of first vector is joined with the head of the second vector. This method of addition is called head to tail rule. The vector joining the tail of first vector to the head of last vector is called resultant vector a Graphical method used to find the resultant of two or more forces is called head to tail rule.

Question: 56

Does the fan satisfy second condition for equilibrium when rotating with uniform speed

Answer: 56

56-123

Yes, It satisfy because moment arm is zero than

Question: 57

Does the speed of a ceiling fan go on increasing all the time.

Answer: 57

57-123

No, speed of a ceiling fan is not increasing all the time but it is constant.

Question: 58

Can force be added by ordinary addition of number

Answer: 58

58-123

No, forces cannot be added by ordinary addition of number They can be added by head to tail rule because force is vector quantity

Question: 59

The weight of the ladder in fig produces an anticlock wise toruqe

Answer: 59

59-123

Yes, the ladder is in state of equilibrium.

Question: 60

On doubling the moment arm, what will be its effect on the value of torque

Answer: 60

60-123

On doubling the moment arm the value of torque will also be double

Question: 61

Discuss centre of gravity of some symmetrical object

Answer: 61

61-123

Uniform rod, Square plate and rectangular plate, Uniform circular disc, Uniform solid sphere, Triangular plate, Uniform solid or hollow cylinder,

Question: 62

At which point an applied force does not produce rotation

Answer: 62

62-123

A force applied at the centre of mass of a body does not produce any rotation rather the body moves in the direction of applied force

Question: 63

Write the types of parallel forces

Answer: 63

63-123

There are two types of parallel forces.

Like parallel force

Unlike parallel force

Question: 64

A ladder leaning at a wall as shown in figure is in equilibrium how

Answer: 64

64-123

The weight of ladder produces anticlock wise torque. The wall pushes the ladder at its tope end thus produce a clockwise torque. Both torques are equal and opposite and cancel their effect. So, the ladder is in state of equilibrium.

Question: 65

Define trigonometry

Answer: 65

65-123

The branch of geometry which explains the properties of right angle triangle is called trigonometry.

Question: 66

Define Resolution of forces

Answer: 66

66-123

Forces into their component forces is called resolution of forces

Question: 67

What is the second condition of equilibrium

Answer: 67

67-123

First condition of equilibrium: A body is said to satisfy first condition for equilibrium if the resultant of all the forces acting on it is zero,

Formula F=0

Question: 68

Give an example of a moving body which is in equilibrium?

Answer: 68

68-123

A paratroopercoming down with terminal velocity is in equilibrium this type of equilibrium.

Question: 69

Define equilibrium and give its example

Answer: 69

69-123

Equilibrium: A body is said toi be in equilibrium if no net force acts on it

Question: 70

Define couple arm

Answer: 70

70-123

The perpendicular distance between two force of couple is called couple arm

Question: 71

Where are the centre of gravity of uniform square and uniform triangular sheets.

Answer: 71

71-123

Centre of gravity of a square of a rectangular Square: The centre of a gravity of a uniform square or a rectangular sheet is the point of intersection of its diagonals

Question: 72

What is right angle triangle

Answer: 72

72-123

A triangle having an angle of 90 in it is called Right angle triangle.

Question: 73

What is perpendicular

Answer: 73

73-123

The line facing the angle in a right angle triangle is called perpendicular e.g the side BC in the figure is perpendicular

The line have 90 angle with any plane is called perpendicular

Question: 74

Define couple and couple arm?

Answer: 74

74-123

A couple is formed by two unlike parallel forces of the same magnitude, but not along the same line

Question: 75

What is hypotenuse

Answer: 75

75-123

The facing the angle of 90 is called hypotenuse e.g the side AC in the figure is hypotenuse

In right angle triangle the side opposite to right angle is called hypotenuse

Question: 76

What is line of action force

Answer: 76

76-123

A line along which a force acts is called line of action of the force

Question: 77

Define rigid body and give an example

Answer: 77

77-123

Rigid Body: A body is composed of large number of particles. It the distance between all pairs of particles of the body do not change by applying a force, then it is called a rigid body

Question: 78

A force of 150 N is making an angle of 40 with horizontal surface what is its vertical components.

Answer: 78

78-123

Given data: Give data F= 15N

0=40

Question: 79

Why a body regain its previous state in stable equilibrium

Answer: 79

79-123

Because in stable equilibrium its centre of gravity is at the lowest position

Question: 80

What is base

Answer: 80

80-123

The smaller side of right angle triangle with angle is called base e,g the side AB in the figure is base.

Question: 81

What is meant by perpendicular components

Answer: 81

81-123

Perpendicular Component: Those components which makes an angle of 90 with each other are called perpendicular components. The perpendicular components of force is fx and fy

Question: 82

Define axis of rotation

Answer: 82

82-123

The line about which a body rotates is called axis of rotation

Question: 83

Force of 150N can loosen a nut when applied at end of a spanner 10cm long

Answer: 83

83-123

Given data: F=150N

L=10cm=01.m

Question: 84

Why a body does not regain its previous state in unstable equilibrium

Answer: 84

84-123

Because in this state centre of gravity of body is at highest position.

Question: 85

Define unstable equilibrium

Answer: 85

85-123

Unstable Equilibrium: If a body does not return to its previous position when set free after a slightest tilt is said to be in unstable equilibrium

Question: 86

Define resolution of vectors

Answer: 86

86-123

To split up a force into its perpendicular components is called resolution of forces.

Question: 87

Define torque and Center of mass

Answer: 87

87-123

Torque: The turning effect of a force is called torque or moment of the force

Question: 88

Explain couple with the help of an example

Answer: 88

88-123

Couple A Couple is formed act on a steering wheel and produce torque to torque to turn the vehicle

Question: 89

On which factor torque depends

Answer: 89

89-123

So, torque depends upon force and moment arm

Question: 90

What is state of neutral equilibrium

Answer: 90

90-123

Neutral Equilibrium: If a body remains in its new position when disturbed from its previous position then body is said to be in neutral equilibrium

Question: 91

How head to tail rule helps us to find resultant of vectors

Answer: 91

91-123

To determine resultant vector by head to tail rule we have to draw the resultant vector from head of last to tail of 1st vector It given us resultant graphically

Question: 92

What is line of action of force

Answer: 92

92-123

Line of action of force and moment arm always makes angle 90 with each other

Question: 93

Define resultant of forces and explain by diagram

Answer: 93

93-123

Resultant of forces: A resultant force is a single force that has the same effect as the combined effect of all the force to be added

Question: 94

Differentiate between torque and couple

Answer: 94

94-123

Torque: Turing effect of force is called torque .

To produce a torque we need only one force at least

Torque or moment of force is equal to product of force F and moment arm L

Question: 95

Define parallel forces. Write n names of its types

Answer: 95

95-123

Parallel forces: Such forces which are parallel to each other are called parallel forces.

Question: 96

Why the height of vehicles is kept as low as possible?

Answer: 96

96-123

We Know that smaller the height of center of gravity of a body , greater will be its stability . The height of vehicles is kept low to lower their center of gravity and as a result their stability increases.

Question: 97

Define center of gravity

Answer: 97

97-123

Resultant vector: A resultant vector is a single vector that the same effect as the combined effect of all the vectors be added

Question: 98

Differentiate between Axis of rotation and Mometn

Answer: 98

98-123

Axis of rotation The straight line passing through a body about which the body can rotate is called axis of rotation

Question: 99

What is meant by graph

Answer: 99

99-123

A graph is a diagram showing the relationship between variable quantities typically of two variables, each measured along a pair of axis at right angle.

Question: 100

Define like and unlike parallel forces

Answer: 100

100-123

Like parallel forces: Like parallel forces are the forces that are parallel to each other and have the same direction

Question: 101

Define like parallel forces and moment arm

Answer: 101

101-123

Like parallel forces: Like parallel force are the forces that are parallel to each other and have the same direction

Question: 102

What is Plumb line

Answer: 102

102-123

Plumb line: A plumb line consists of a small metal bob lead or brass supported by a string. When the bob is suspended freely by the string, it rests the vertical direction due to its weight acting vertically down ward.

Question: 103

Think of a body which is at rest but not in equilibrium

Answer: 103

103-123

A body thrown vertically upward at maximum height is at rest for a while but at that moment gravitational force

Question: 104

Define plumb line?

Answer: 104

104-123

A plum be line is a piece of string with a weight attached to the end that is used to check that something such as wall is vertical

Question: 105

Differentiate between clockwise and anti-clockwise moment

Answer: 105

105-123

Clockwise Moment: The force that trrns a spanner in the clockwise direction is known is clockwise force. The torque or moment of force produced to this force is called clockwise moment

The moment produced during tighten a nut

Question: 106

What is meant by Rigid body

Answer: 106

106-123

Rigid Body: A body is composed of large number of small particles. If the distance between all pairs of particles of the body do not change by applying of force the, it is called rigid body A rigid body is the one that is not deformed by force or forces acting on it

Question: 107

Define Resultant vector?

Answer: 107

107-123

A resultant vector is a single force that has the same effect as the combined effect of all the forces to be added.

Question: 108

Define Centre of mass of a body

Answer: 108

108-123

Centre of mass: The point where when the force is applied, the system move without rotation is called centre of mass.

Question: 109

Why door is easy to open or close by pushing or pulling at handle?

Answer: 109

109-123

We open or close a door by pushing it . Here push or pull turn the door about its hinge or axis of rotation, The door is opened or closed due to the turning effect of the force acting on it.

Question: 110

Define equilibrium

Answer: 110

110-123

Equilibrium: A body is said to be in equilibrium if no net force acts on it. A body in equilibrium thus remains at rest or moves with uniform velcity

Question: 111

Difference between like and unlike forces?

Answer: 111

111-123

Like forces:

like forces are the forces that are parallel to each other and have the same direction

Question: 112

What is meant by Couple of forces

Answer: 112

112-123

Couple: A Couple is formed by two unlike parallel forces of the same magnitude but not along the same line.

Question: 113

Head to tale rule explain?

Answer: 113

113-123

Draw the representative lines of all the vector to be added in such a way that head of first vector coincides with the tail of second vector, head of second vectorcoincides with the tail of third vector and on so

Question: 114

Why are vehicles made heavy at the bottom

Answer: 114

114-123

Vehicles are made heavy at the bottom to lower their centre of gravity to keeps the balanced vehicles.

Question: 115

What is meant by additionof forces?

Answer: 115

115-123

Force is a vector quantity. It has magnitude as well direction; therefore forces are not added by ordinaryarithmetic rules. They are added by a method known as head to tail rule.

Question: 116

Define first condition of equilibrium?

Answer: 116

116-123

A body will be in equilibrium if the resultant of all the forces acting on it is zero this is first condition of equilibrium.

Question: 117

Write the principle of moments

Answer: 117

117-123

State the principle of moments: A body initially at rest does not rotate if the sum of all the clockwise moments acting on it balanced by the sum of all the anti clockwise moment acting on it This principle is known as the principle of moments. Mathematically clockwise moments=Anti-clockwise moments

Question: 118

What is difference between stable and unstable

Answer: 118

118-123

Stable: equilibrium: A body is said to be in stable equilibrium if after a slight tilt it return to its previous position.

Question: 119

Why a body cannot be in equilibrium due to a single force acting on it

Answer: 119

119-123

A body cannot be in equilibrium due to a single force because a single force cannot be considered zero as a net force and the torque produced by it will also not be zero

Question: 120

Define parallel forces and types?

Answer: 120

120-123

In a plane, if number of forcesact on a body such that their points of action are different, but lines of action are parallel to each other, then these forces are called parallel forces.

There are two types of parallel forces

1- like parallel forces, unlike parallel forces

Question: 121

Difference between Center of mass and center gravity?

Answer: 121

121-123

Center of mass.

Center of mass of a system is such a point where an applied force cause the system to move without rotation

Question: 122

Why the height of vehicles is kept as low as possible

Answer: 122

122-123

The height of vehicles is kept as low as possible to make them more and more stable because stability increased as height of vehicle decrease.

Question: 123

What is meant by resolution of forces?

Answer: 123

123-123

The decomposition or division of a vector into itscomponent is called resolution of a vector or force

Physics Chapters

9th Class Chapter 4 Physics Short Questions

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