Kinematics

9th Class Physics Chapter 2 Exercise Short Questions with Answers

Q 2.2 : Explain translatory motion and give examples of various types of translatory motion .

Translatory Motion :

” The motion in which a body moves along a line (straight or curved ) without any rotation , is called translatory motion .”

Types of Translatory Motion :

Circular motion
Linear motion
Random motion

1 . Circular Motion :

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

Example : A car moving along a circular track .

2 . Linear Motion :

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

Example : Aero-plane flying straight in the air is linear motion .

3 . Random Motion :

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

Example :Motion of insects and birds is random motion .

Q 2.3 :Differentiate between the following .

i .

Rest	Motion
→A body is said to be at rest , if it does not change its position with respect to its surroundings .	→ A body is said to be in motion , if it changes its position with respect to its surroundings .
Example	Example
→A passenger sitting in a moving bus is at rest because he \ she is not changing his\her position with respect to other passengers or objects in the bus .	→To an observer outside the moving bus , the passenger and the other objects inside the bus are in motion .

ii.

Circular Motion	Rotatory Motion
→The motion of an object in a circular path is known as circular motion .	→The spinning motion of a body about its axis is called its rotatory motion .
→In circular motion , the point about which a body goes around is outside the body .	→In rotatory motion , the line around which a body moves about is passing through the body itself .
Example	Example
→Motion of earth around the sun . →A toy train moving in a circular track.	→Motion of earth about its geographical axis . →Motion of top around its axis .

iii.

Distance (S)	Displacement (d)
” Total length of a path between two points is called distance between these two points .”	“The shortest distance between two points is called displacement .”
→Distance is a scalar quantity .	→Displacement is a vector quantity.

iv.

Linear Motion	Random Motion
” Motion of a body along a straight line is called linear motion .”	” The disordered or irregular motion of an object is called random motion .”
Example	Example
Free falling object	Motion of gas molecules

vi.

Scalers	Vectors
“A scaler quantity is described completely by its magnitude .”	” A vector quantity is described completely by its magnitude and direction .”
Example	Example
Mass , Length , time , speed , volume , work , energy	Velocity , force , displacement , motion , torque

Q 2.4 : Define the term speed , velocity and acceleration .

Speed (v):

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

Velocity (v) :

” The rate of change of displacement is called velocity .”

Acceleration (a) :

Q 2.5 : Can a body moving at a constant speed have acceleration .

Yes , A body moving at a constant speed have acceleration .

Condition :

If a body is changing its direction then it has acceleration acting towards Centre provided by centripetal force .

Q 2.6 : How do riders in a Ferris wheel possess translatory motion but not rotatory motion ?

Riders in Ferris wheel have circular motion (a type of translatory motion ).

Reason :

Because their motion is in a circle without rotation .
And the line about which wheel riders goes around , lies outside the body .

Q 2.7 : Sketch a distance-time graph for a body starting from rest . How will you determine the speed of a body from this graph ?

Q 2.8 : What would be the shape of a speed-time graph of a body moving with variable speed ?

The shape of velocity-time graph is zigzag i.e., not a straight line , when the body is moving with variable speed .

Q 2.9 : Which of the following can be obtained from speed-time graph of a body ?

i . Initial speed

ii . Final speed

iii . Distance covered

iv . Acceleration of motion

All the above quantities can be obtained from speed-time graph of a moving body .

Q 2.10 : How can vector quantities be represented graphically ?

Graphical representation of Vector :

Graphically , a vector can be represented by a line segment with an arrow head .

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Q 2.11 : Why vector quantities cannot be added and subtracted like scalar quantities ?

vector quantities cannot be added and subtracted like scalar quantities.

Reason : Vector quantities have direction and quantities having direction cannot be added and subtracted like scalar quantities .

Q 2.12 : How are vector quantities important to us in our daily life ?

Vector quantities are very important to us in our daily life .

Vector quantities help us to determine position / direction of any place .

Example : Pilots use vectors to detect their destination .

Q 2.13 : Derive equations of motion for uniformly accelerated rectilinear motion .

Q 2.14 : sketch a velocity-time graph for the motion of the body . From the graph explaining each step , calculate total distance covered by the body .