# 9th Class Physics: Chapter 2 Kinematics Short Questions Answers

## 9th Class Physics: Chapter 2 Kinematics Short Question Answers

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Translatory Motion: The in which a body moves along a line without any rotation is called translatory motion.

In translatory motion the line may be straight or curved.

Types of Translatroy Motion: There are three types of Translatory Motion.

(a) Circular motion (b) Linear motion (c) Random motion

(a) Circular Motion:

The motion of an object in a circular path is known as circular motion.

Examples:

(a) A bicycle or a car moving along a circular track.

(b) The riders in a moving ferries wheel have circular motion.

(b) Linear Motion:

Straight line motion of a body is known as its linear motion.

Examples:

(a) Aeroplane flying straight in air is an example of linear motion

(b) Objects falling vertically down is an example of linear motion

(c) Random Motion:

The disordered or irregular motion of an object is called random motion.

Example:

(a) The motion of insects and birds is random motion.

(b) The motion of dust or smoke particles in the air is random motion.

(i) Initial speed

(ii) Final speed

(iii) Distance covered in time t

(iv) Acceleration of motion

All the given factors can be obtained from speed-time graph of a body.

Yes body moving at constant speed has acceleration if it changes its direction or moving in a circular path.

In circular motion the point about which a body goes around, is outside the body. In rotatory motion the line about which a body moves is passing through the body itself.

Riders in a ferris wheel have rotatory motion because the axis about which a rider moves is passing through the rider itself.

Scalar quantities are the quantities which can be described completely by magnitude while vector quantities need direction and magnitude for their complete description.

The quantities having direction cannot be added and subtracted like scalar quantities.

Vector quantities are important to us in our daily life because a vector can be described completely by magnitude along with its direction. Examples of vectors are velocity, displacement, force, momentum, torque, etc. It would be meaningless to describe vectors without direction. For example, distance of a place from reference point is insufficient to locate that place. The direction of that place from reference point is also necessary to locate it.

Kinematics is the study of an object without discussing the cause of motion.

Rest:

A body is said to be at rest, if it does not change its position with respect to its surroundings.

Trees around the bank of the road are in rest position.

Motion:

A body is said to be in motion, if it changes its position with respect to its surroundings.

A moving bus on the road is in a state of motion.

Linear Motion:

Straight Line motion of a body is known as its linear motion.

Aeroplane flying straight in air and objects falling vertically down are the examples of the linear motion.

Random motion:

• The disordered or irregular motion of an object is called random motion.

• The motion of dust or smoke particles in the air is the example of random motion.

Circular Motion:

The motion of an object in a circular path is known as circular motion.

Motion of the earth around the sun and motion of the moon around the earth are examples of circular motion.

Rotatory Motion:

The spinning motion of a body about its axis is called its rotatory motion.

The motion of the earth about its own axis is rotatory motion.

The motion of a bicycle wheel about its axis is also rotatory motion.

Circular motion:

The motion of an object in a circular path is known as circular motion.

Random motion:

The disordered or irregular motion of an object is called random motion.

Circular Motion:

The motion of an object in a circular path is known as circular motion.

Motion of the earth around the sun and motion of the moon around the earth are examples of circular motion.

Vibratory Motion:

To and fro motion of a body about its mean position is known as vibratory motion.

Up and down movement of the children in a see-saw is an example of vibratory motion.

Linear Motion:

Straight line motion of a body is known as its linear motion.

Circular Motion:

The motion of an object in a circular path is known as circular motion.

Transatroy motion:

The in which a body moves along a line without any rotation is called translatory motion.

In translatory motion the line may be straight or curved.

Circular Motion:

The motion of an object in a circular path is known as circular motion.

Motion of the earth around the sun and motion of the moon around the earth are examples of circular motion.

Translatory Motion:

The in which a body moves along a line without any rotation is called translatory motion.

In translatory motion the line may be straight or curved.

Example: A car moving in a straight line has translatory motion.

Rotatory Motion:

The spinning motion of a body about its axis is called its rotatory motion.

The top spins about its axis passing through it and thus it possesses rotatory motion.

An axis is a line around which a body rotates.

Vibratory Motion:

To and fro motion of a body about its mean position is known as vibratory motion.

Consider the motion of a baby in a swing. It moves back and forth about its mean position. The motion of the baby repeats from one extreme to other extreme with the swing.

Scalars:

• A Scalar is described completely by its magnitude only.

• Mass, length, time, speed, volume, work and energy are some examples of scalars.

Vectors:

• A vector is described completely by its magnitude and direction.

• Velocity, displacement, force, momentum and torque are some example of vectors.

Speed:

The distance covered by an object in unit time is called its speed.

Speed can be calculated by given formula.

Speed = distance/time

Speed is a scalar quantity. Because it can be described completely by a magnitude only.

Velocity:

The rate of displacement of a body is called its velocity.

Velocity can be calculated by given formula.

Velocity = displacement/time taken

Velocity is a vector quantity. Because it can be described completely by a magnitude and direction.

Distance:

• Length of path between two points is called the distance between those points.

• Distance is a scalar quantity because it can be completely described with the help of magnitude only.

Displacement:

• Displacement is the shortest distance, between two points which has magnitude and direction.

• Displacement is a vector quantity because it can be completely described with the help of magnitude and direction.

A body has uniform acceleration if it has equal changes in velocity in equal intervals of time however short the interval may be.

Acceleration is defined as the rate of change of velocity of a body.

Acceleration can be calculated as.

Acceleration = Change in velocity/ time taken

Unit of acceleration is meter per second per second ms-2

Total distance = 100m

Total time = 12 sec

Average speed = Total distance/Total time

Average speed = 8.33 ms-1

Variable:

A body has variable speed if it covers equal distance in unequal interval of time however short the interval may be.

Uniform speed:

A body has uniform speed if it covers equal distance in equal interval of time however short the interval may be. OR If the speed of a body does not vary and has the same value then the body is said to posses uniform speed.

36kmh-1 = 36 x 1000/3600ms-1 = 10ms-1

Positive acceleration:

Acceleration of a body is positive if its velocity increases with time.

The direction of this acceleration is the same in which the body is moving without change in its direction.

Negative Acceleration:

Acceleration of a body is negative if velocity of the body decreases.

The direction of negative acceleration is opposite to the direction in which body is moving.

Speed:

The distance covered by an object in unit time is called its speed.

Uniform speed:

A body has uniform speed if it covers equal distance in equal interval of time however short the interval may be. OR If the speed of a body does not vary and has the same value then the body is said to posses uniform speed.

20ms-1 = 20/1000 x 3600 kmh-1= 72000/1000 kmh-1= 72 kmh-1

10ms-1 = 10 x 1000/3600 ms-1= 2.78 ms-1

Velocity:

The rate of displacement of a body is called velocity.

Uniform velocity:

The body has uniform velocity if it covers equal displacement in equal interval of time however the short the interval may be.

If the speed and direction of a body does not change then it posses uniform velocity.

Gravitational Acceleration:

The acceleration of freely falling bodies is called gravitational acceleration. It is denoted by g.

Value of g: On the surface of the Earth, the value of g is approximately 10ms-2.

For bodies falling freely g is positive.

For bodies moving up g is negative.

Second Equation of motion: S = vit +1/2 x at2

Third Equation of motion: 2aS = vf2 – vi2

Velocity:

The rate of displacement of a body is called its velocity.

Velocity can be calculated as v = d/t

Unit of velocity is meter per second.

Acceleration:

Acceleration is defined as the rate of change of velocity of a body.

Acceleration can be calculated as.

Acceleration = Change in velocity/ time taken

Unit of acceleration is meter per second per second ms-2

Position: Position means the location of a certain place or object from a reference point. OR The term position describes the location of a place or a point with respect to some reference point called origin.

Explanation: If someone wants to describe the position of his/her school from home Let the school be represented by S and home by H as shown in the figure.

The position of the school from home will be the distance and is represented by a straight line HS in the direction from H to S as shown in given figure below.

Graphically a vector can be represented by a line segment with as arrow head. In the given figure the line AB with arrowhead at B represents a vector v.

The length of the AB gives the magnitude of vector v on a selected scale.

While the direction of the line from A to B gives the direction of the vector v.

Object is moving with constant speed.

The speed of an object is said to be constant if it covers equal distance in equal interval of time. The distance-time graph as shown in the figure is a straight line. It slope gives the speed of the object. Consider two points A and B on the graph:

Speed of the object = Slope of line AB.

Speed of object = distance EF/time CD

Speed of object= 20/10=2ms-1

The speed found from the graph is 2ms-1.

When a body is moving with variable speed, the shape of its speed-time graph is not a straight line.