Physics Class 9 Chapter 2 (Exercise Solution)
UNIT No. 2
Kinematics
Exercise
2.1
Encircle the correct answer from the given choices.
i.
A body has translatory motion if it moves along a
(a) straight
line
(b) circle
(c) line
without rotation
(d) curved path
ii.
The motion of a body about an axis is called
(a) circular
motion
(b) rotatory
motion
(c) vibratory
motion
(d) random
motion
iii.
Which of the following is a vector quantity?
(a) speed (b) distance (c) displacement (d)
power
iv.
If an object is moving with constant speed, then its distance-time
graph will be a straight line.
(a) along
time-axis
(b) along
distance-axis
(c) parallel to
time-axis
(d) inclined to
time-axis
v.
A straight line parallel to time-axis on a distance-time graph
tells that the object is
(a) moving with
constant speed
(b) at rest
(c) moving with
variable speed
(d) in motion
vi.
The speed-time graph of a car is shown in the figure, which of the following
statement is true?
(a) car has an
acceleration of 1.5 m-2
(b) car has
constant speed of 7.5 ms-1
(c) distance
travelled by the car is 75 m
(d) average
speed of the car is 15 ms-1
vii.
Which one of the following graphs is representing uniform
acceleration?
viii.
By dividing displacement of a moving body with time, we obtain
(a) speed (b) acceleration (c) velocity (d) deceleration
ix.
A ball is thrown vertically upward. Its velocity at the highest
point is:
(a) -10 ms-1 (b)
zero (c) 10 ms-2 (d) none of these
x.
A change in position is called:
(a) speed (b)
velocity
(c)
displacement (d)
distance
xi.
A train is moving at a speed of 36 kmh-1. Its speed
expressed in ms-1 is:
(a) 10 ms-1
(b) 20 ms-1 (c)
25 ms-1 (d) 30 ms-1
xii.
A car starts from rest. It acquires a speed of 25 ms-1
after 20 s. The distance moved
by the car during this time is:
(a) 31.25 m (b) 250 m (c)
500 m (d) 5000 m
Answers of
Multiple Choice Questions (MCQs)
|
i.
|
(c) |
ii.
|
(b) |
|
iii.
|
(c) |
iv.
|
(d) |
|
v.
|
(b) |
vi.
|
(c) |
|
vii.
|
(a) |
viii.
|
(c) |
|
ix.
|
(b) |
x.
|
(d) |
|
xi.
|
(a) |
xii.
|
(b) |
2.2
Explain translatory motion and give examples of various types of
translatory motion?
Translatory Motion
“In
translational motion, a body moves along a line without any rotation. The line
may be straight or curved”
Translatory motions
can be divided into three types as given below
i.
Linear Motion,
ii.
Circular Motion
iii.
Random Motion
i.
Linear Motion
“Straight line motion
of a body is known as its linear motion.”
For Example:
·
a
car moving on a straight and level road is linear motion.
·
Aeroplanes
flying straight in air.
·
objects
falling vertically down
ii.
Circular Motion
“The
motion of an object in a circular path is known as circular motion”
For Example:
·
A
car moving along a circular track possesses circular motion
·
Motion
of the Earth around the Sun
·
Motion
of the moon around the Earth.
iii.
Random Motion
“The
disordered or irregular motion of an object is called random motion.”
For Example:
·
Motion
of insects and birds is random motion
·
The
motion of dust or smoke particles in the air is also random motion.
·
The
Brownian motion of a gas or liquid molecules along a zig-zag
path is also an example of random motion.
2.3
Differentiate between the following:
i.
Rest
and motion.
ii.
Circular
motion and rotatory motion.
iii.
Distance
and displacement
iv.
Speed
and velocity.
v.
Linear
and random motion.
vi.
Scalars
and vectors.
i.
Rest and motion
Rest:
A
body is said to be at rest if it does not change its position with respect to
its surroundings.
Motion:
A body is said to
be in motion if it changes its position with respect to its
surroundings.
ii.
Circular motion and rotatory motion.
|
Sr. No. |
Circular Motion |
Rotatory
Motion |
|
1 |
The motion of an
object in a circular path is known as circular motion. For Example: ·
A
car moving along a circular track possesses circular motion ·
Motion
of the Earth around the Sun ·
Motion
of the moon around the Earth. |
The spinning
motion of a body about its axis is called its rotatory motion. For Example: ·
The
motion of a wheel about its axis. ·
The
motion of the Earth about its ·
The
motion of a top |
|
2 |
In circular motion, the point about |
In rotatory motion, the line (axis),
around which a body moves about, is passing through the body itself. |
|
3 |
|
|
iii.
Distance and displacement
|
Sr. No. |
Distance |
Displacement |
|
1 |
Length of a path
between two points is called the distance between those points. |
Displacement is the shortest distance between two points which
has magnitude and direction. |
|
2 |
Distance is a scalar quantity, |
Displacement is a vector quantity. |
|
3 |
It is denoted by S. |
It is denoted by d. |
iv.
Speed and velocity
|
Sr. No. |
Speed |
Velocity |
|
1 |
The distance
covered by an object in unit time is called its speed. Speed = Distance
covered/Time Taken |
The
rate of displacement of a body is called its velocity Speed = Displacement/Time Taken. |
|
2 |
Speed is a scalar quantity, |
Velocity is a vector quantity. |
|
3 |
It is denoted by v. |
It is denoted by v. |
v.
Linear and random motion.
Linear Motion
“Straight line motion
of a body is known as its linear motion.”
For Example:
·
a
car moving on a straight and level road is linear motion.
·
Aero planes
flying straight in air.
·
objects
falling vertically down
Random Motion
“The disordered
or irregular motion of an object is called random motion.”
For Example:
·
Motion
of insects and birds is random motion
·
The
motion of dust or smoke particles in the air is also random motion.
·
The
Brownian motion of a gas or liquid molecules along a zig-zag
path is also an example of random motion.
vi.
Scalars and vectors.
Scalars
A physical
quantity which can be completely described by its magnitude is called a scalar.
Examples: mass,
length, time, speed, volume, work and energy.
Vectors
A vector
quantity is described completely by magnitude and direction.
Examples:
velocity, displacement, force, momentum, torque, etc.
2.4
Define the terms speed, velocity, and acceleration.
Speed
“The distance covered by an object in unit time is called its
speed.”
\[Speed=\frac{Distance Covered}{Time Taken}\]
\[v=\frac{S}{t}\]
Speed
is a scalar quantity. SI unit of speed is metre per second (ms-1).
Velocity
“The rate of displacement of a body is called its velocity”
\[velocity=\frac{Displacement}{Time Taken}\]
\[\overline{v}=\frac{\overline{d}}{t}\]
velocity is a vector quantity. SI unit of speed is metre per second (ms-1).
Acceleration
“Acceleration is defined as the rate of change of
velocity of a body.”
\[acceleration=\frac{Change in velocity}{Time Taken}\]
\[acceleration=\frac{final velocity - initial velocity}{Time Taken}\]
\[\overline{a}=\frac{\overline{v_{f}}-\overline{v_{i}}}{t}\]
acceleration is a vector quantity. SI unit of acceleration is metre per second per second (ms-2).
2.5
Can a body moving at a constant speed have acceleration?
Yes, a body moving at
constant speed has acceleration if it moves along a circular track because the
direction of motion of a body along a circular track is continuously changing.
2.6
How do riders in a Ferris wheel possess translatory motion but not rotatory motion?
Rider in a Ferris wheel possess circular motion because they are moving
in a circle of constant radius. As circular motion is a type of translatory
motion. Therefore, riders in a Ferris wheel possess translatory motion.
As Rider in a Ferris wheel are not moving about their axis, therefore
Rider in a Ferris wheel does not possess rotatory motion.
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?
Distance time graph of a body starting at rest is
shown in the figure below
\[Speed of the object= Slope of line AB\]
\[Speed of the object=\frac{Distance EF}{Time CD}\]
\[Speed of the object=\frac{20 m}{10 s}\]
\[Speed of the object= 2 ms^{-1}\]
2.8
What would be the shape of a speed -time graph of a
body moving with variable speed?
The shape of speed-time graph of a body moving with
variable velocity is not a straight line.
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 in time t.
(iv) Acceleration of motion.
All of these can be measured by speed-time graph.
2.10 How can vector
quantities be represented graphically?
Graphically, a vector
can be represented by a line segment with an arrowhead. The length of the line
gives the magnitude of the vector on a selected scale. While the direction of
the line gives the direction of the vector.
2.11 Why vector quantities
cannot be added and subtracted like scalar quantities?
Scalars quantities are
added or subtracted by simple arithmetic methods because scalar quantities have
no direction. Since vectors have magnitude as well as direction, therefore
vectors cannot be added and subtracted by simple arithmetic methods like
scalars. Vectors are added by head to tail rule,
2.12 How are vector
quantities important to us in our daily life?
Sometimes it would be meaningless to describe some
quantities without directions therefore vectors quantities are very important
in our daily life.
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 that place.
2.13 Derive equations of motion for uniformly accelerated rectilinear motion.
First (1st) equation of motion
Second (2nd) equation of motion
Third (3rd) equation of motion
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..
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