9th Class Physics Chapter 2 Short Questions with Answers Solved

Question: 1

Define Velocity

Answer: 1

1-19

Velocity: The displacement covered by a body in unit time is called velocity. It is denoted by v.

Example: For example, a car is moving with a velocity of 50 m/s. towards east. so, in case of velocity, we specify both magnitude and direction.

Mathematical form: Velocity = displacement/ time

Question: 2

Does a speedometer measure a car's speed or velocity?

Answer: 2

2-19

As we know that speed is a scalar quantity . It has magnitude only but having no direction while velocity is a vector quantity and it has magnitude as well as direction. The speedometer of a car displays only magnitude i.e. speed of a car but it does not tell us about the direction of the car. Thus, the speedometer measures only the speed of the car but not its velocity.

Question: 3

Difference between Distance and Displacement.

Answer: 3

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Distance: The length of actual path traveled by a body between two positions is called distancde travelled.

Displacement: The shortest directed distance between two positions is called displacement.

Question: 4

Define scalar and vector quantities.

Answer: 4

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Scalar Quantities: Those physical quantities which are completely decribed by their magnitude only are called scalar quantities or scalar

The scalar can be added, subtrated, multiplied and dividd by ordinary mathematical method.

Examples: Speed, distance, temperature, energy, volume, power ec. are the examples of scalar quantities.

Question: 5

Explain different types of motion and give an example of each.

Answer: 5

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Types of Motion:

In general, there are three types of motion whihc are described below:

1- Translatory Motion 2- Rotatory Motion 3- Vibratory Motion.

Question: 6

Prove that 2as =Vf2 - Vi2

Answer: 6

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Consider a body is moving with initial velocity " vi" covered disance "S" in time "t"

The distance covered by a body is equal to of " OABC" which is known as Trapezium

In the figure

Initial velocity = Vi = OA = DC

Final velocity = Vi = BC

Time = t = OC = AD

Acceleration = a = AB

Distance = S

from the figure

Distance travelled = Area of figure OABC

S = Area of Trapezium OABC

S= (Sum of prallel sides ) x hieght/2

S= (OA +BC) x OC/2

S = (vi+Vf) x t/2

S = (Vf +Vi)/2 x t ............... (i)

As from 1st equation of motion

Vf = Vi +at

put it in eq (i0

S = (Vf +Vi/1( Vf-Vi/a)

S = Vf2 - Vi2/2a

2aS = Vf2 - Vi2

Question: 7

Use velocity time graph to prove the following equation of motion.

Vf= Vi + at

Answer: 7

7-19

1st equation of motion : Consider a body has initial velocty " vi" at point 'A" and then its velocity changes with uniform acceleration from "A" to "B" in time interval "t" and its final veocity becomes "Vf" as shown

In the figure

Initial velocty = vi = OA --=DC

Final Velocity = Vf =BC

Time = t = OC =AD

Acceleration =a = AB

From the graph

BC = BD +DC .............(i)

Put the values of "BC" and "DC" in equation (i)

Vf = BD + VI..................(ii)

As we know that the slope of velocity time graph is equal to accelertion, then

AB = BD/AD

a = BD/t

at= ND

Put it in equ (ii0

Vf = at +Vi

Vf = Vi +at

Question: 8

Define Acceleration

Answer: 8

8-19

Acceleration: Time rate of change of velocity is called acceleration.

Mathematicla form:

Acceleration = Change in velocity / time

Question: 9

A person standing on a roof of a building throws a rubber ball down with a velocity of 8.0 m/s. What is the acceleration of the ball?

Answer: 9

9-19

When 9.8 m/n a pwrson throws a ball from the top of a building the ball will fall towards earth due to fore of gravity. According to famous scientist Galiteo all bodies falling towards earth with a constant acceleration of g =9.8 m/s2 So, if we ignore the air resistance, than the ball will fall freely with acceleration due to gravity "g" its magnitude will be 9.8 m/s2 and it will be directed towards earth.

Question: 10

Explain Speed, Velocity, Acceleration

Answer: 10

10-19

Speed: The distance covered by a body in a unit time is called speed . It is denoted by "V"

Mathematical form:

Speed = distance /time

Quantity and Unit:

Speed is a scalar quantity and its SI unit is meter per seond

Example: For example, a car is moving with a speed of 50 m/s. This means that is every one second, it covers a distance of 50 m.

Types of speed:

The speed is categorized into following types.

Question: 11

Derive 2nd Equation of Motion.

Answer: 11

11-19

Consider a body is moving with initial velocity "vi" and covered distance "S" in time "t"

The distane covered by a boyd is equalt to the area between velocity -time graph "AB" and time axis "OC" which is equal to the areaof "OABC".

Question: 12

What is motion? Describe that motion is relative.How two observers in relative motion can have conflicting views about same object?

Answer: 12

12-19

Motion: When a boyd changes its position relative to its surrounding then we say that the boyd is in motion.

Example:

1- A flying bird 2- Among car 3- A running boy. etc.

Question: 13

A ball is thrown upward with an initial speed of 5 m/a. Wha twill be its speed when it returns to starting point?

Answer: 13

13-19

If a ball is thrown vertically upward with an initial speed of 5 m/s. then in the absence of air resistance, the ball will return back to its starting point with the samw speed of 5 m/s. Because, in upward and a down ward, the only force acting on ball is gravitational pull of earth.

Question: 14

As a freely falling object speeds up, what is happeningto its acceleration does it increase, decrease or stay the same?

Answer: 14

14-19

In the absence of air resistance, all bodies falling towards earth with a constnat acceleration. So for freely falling objects, the speed of the body increases uniformly at the rate of 9.8 m/s2. Thus, the acceleration of the body does not increase, or decrease but remains constant during free- fall motion. i.e. we take g= 9.8 m/s2 as a constant value for free- fall objects.

Question: 15

Define Rest.

Answer: 15

15-19

Rest: When a body does not change its position with respect to its surronding , then the body is said to be in the state rest.

Examples: 1. A bird sitting on a branch of a tree

2, A student sitting on a chair.

Question: 16

Define Value of "g"

Answer: 16

16-19

The Value of "g" near the earth's surface is approximately "9.8 m/s2" and its value is constant fro all bodies. It is directed downward towards the centre of the earth .

Question: 17

What is free fall?

Answer: 17

17-19

Free Fall : The motion in which air resistance is neglected and the acceleration is nearly consntant is known as free-fall.

Question: 18

Define Kinematics.

Answer: 18

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Kinematics: Kinematics is the branch of physics which deals with the study of motion without going into detail of what causes the motion.

Question: 19

Describe a situation in which speed of an object is constant while velocity is not.

Answer: 19

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A situation in which the speed of an object is constant while the velocity is not constant may be tha tof circular motion. For example, a body moving along a circular path may have a consntatn speed. But its velocity is not constant because the direction of velocity changes at each point continuously during circular motion.

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9th Class Chapter 2 Physics Short Questions

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