Class 9th physics
Chapter No 02
Long Questions
Kinematics:
Terminology: kinematic is derived from the Greek word which means motion.
Definition: kinematicsis the branch of mechanics in which we study about the motion of an object without force.
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Question No : 01
What is rest and motion ? Describe that motion is relative ? How two observer in relative motion can have conflicting views about same object?
Answer :
Motion: if a body change it's position to observer is called motion.
Rest and motion are relative : An object in one situation can be at rest but in other situation the same object can be a notion.
Example: if two person are sitting in a car while they are moving on the road.
They are at rest inside the car to each other while in other situation they are in motion to observer from road side .
Conclusion: Hence rest and motion are relative terms.
Khan
Question No 2
Explain different types of motion and give an example of each ?
Answer
Types of motion: There are three main types of motion.
1) translatory motion : if a body changes its position as whole and the line or path of motion could be straight or curved is called translatory motion.
Example: moving of a car, falling bodies.
It is further divided into three types.
Sub Types
a) linear motion: the motion in straight line is called linear motion.
Example: For example the motion of a free falling body.
b) curvilinar motion:: the circular or curved motion is called curvilinar motion.
Example: motion of cricket ball being hit for six.
c) Random motion: the morning of something without having a proper direction is called random motion.
Or
Irregular motion is called random motion.
Example: For example the motion of gases molecules .
2) Rotatory motion: when each and every point or particle a body moves around fix axis or fixed point is called rotatory motion.
Example: For example the motion of wheel of a cycle.
3) vibratory motion : The back and forth or to and fro motion of a body about its main position is called vibratory motion.
Example: For example waves of water, spring .
Khan
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Question No 03
Define scalar and vector quantities. Explain with example the graphical representation of vector quantities?
Answer
Scalar quantities: Those quantities which require only magnitude are called scalar quantities.
Representation: it is represented by A B C etc .
Examples: mass, length ,time ,speed energy, heat, power and work etc .
Vector quantities: those quantities which require both magnitude and direction are called vector quantities.
Representation: it is represented by A,B,C with an arrow over it ➡️,➡️,➡️
A , B, C.
Graphical representation of a vector quantity: a vector quantity is graphically represented by a straight line with an arrow head and tail .
The straight line represent the magnitude and the arrow represents the direction of the vector.
Khan
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QUESTION No 4
What is position? Explain the difference between distance travelled displacement and displacement magnitude?
Answer
POSITION: the term which describe location of a place or a point with respect to some reference point(origin) is called position.
Example:
For example S represents school in H represent home .
H•..............................•S
Home School
Distance: the length of path between two positions is called distance.
Quantity: Distance has no direction therefore it is a scalar quantity.
Denotation: It is denoted by∆l,∆m, ∆x etc.
SI Unit : The SI unit of distance is meter(m).
Displacement: the shortest directed distance between two positions is called displacement.
Quantity: displacement has direction and therefore it is a vector quantity.
Denotation: it is denoted by ,➡️➡️➡️
∆x,∆r,∆l
SI Unit : The is a unit of displacement is meter (m).
Khan
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Question No 05
State and explain the terms.
a) speed. b) velocity c) acceleration.
We will make three shorts Questions.
a) what is speed?
Answer
Speed: the distance covered by a body in unit time called speed.
Denotation: speed is denoted by V .
Mathematical formula:
speed = distance\Time
Quantity: speed is a scalar quantity.
SI unit of speed: the is a unit of speed is meter per second .
ms-1.
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b) What is velocity?
Answer :
velocity: the displacement covered by a body in unit time is called velocity.
Quantity: velocity is vector quantity.
Denotation: velocity is denoted by V and a small arrow over it .
Mathematical formula:
Velocity= Displacement/ Time
SI Unit : The SI unit of velocity is meter per second .
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c) what is acceleration?
Answer
Acceleration: The velocity covered by a body in unit time is called acceleration.
Quantity: acceleration is vector quantity.
Denotation: acceleration is denoted by (a) and an small arrow over it .
Mathematical formula:
Acceleration= change in Velocity/Time .
SI unit: The is a unit of acceleration meter per second square.
a = ms-2
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Question No 06
What are the equations of motion?
Answer
The following are the equations of motion.
1st equation of motion: The first equation of motion relates Vf ( final velocity) Vi ( initial velocity) and time.
Mathematically:
Vf = Vi +at
2nd equation of motion: The second equation of motion relates
displacement(s) with Vi ( initial velocity) and acceleration (a) in time (t) .
Mathematically:
.
S= Vit+1/2at*2
3rd equation of motion: The third equation of motion relates acceleration displacement with final velocity and initial velocity.
Mathematically:
2as= Vf*2-Vi*2
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Question No 07
What is free fall what is its value near the surface of Earth . Explain with example that rock in sheet of paper will fall at the same rate without air resistance.
Answer
Free falling motion: the motion of an object under the action of gravity in which the air resistance is neglected and the acceleration is nearly constant is called free falling motion.
Value near earth surface: the value of free falling motion is 9.8ms-2 (meter per second square ) .
Example: when the air resistance is neglected then both the rock and the sheet of paper will have the same acceleration due to gravity or free fall motion 9.8m/s2..
