UNIT

06 MOTION

LEARNING OBJECTIVES
Students will be able to
‰ List the objects which are at rest and which are in motion around them.
‰ Understand distance and displacement.
‰ Determine the displacement and distance covered by an object describing a
circular path .
‰ Classify the motion of vehicles as uniform motion and non-uniform motion.
distinguish between speed and velocity.
‰ Relate accelerated and unaccelerated motion.
‰ Deduce the equations of motion of an object from velocity – time graph.
‰ Write the equations of motion for a freely falling body.
‰ Understand the nature of circular motion.
‰ Identify centripetal force and centrifugal force in day to day life.

TEXT BOOK EXERCISES

I. Choose the correct answer :
1. The area under velocity – time graph represents the
(a) velocity of the moving object. (b) displacement covered by the moving object.
(c) speed of the moving object. (d) acceleration of the moving object.

2. Which one of the following is most likely not a case of uniform circular motion?
(a) Motion of the Earth around the Sun.
(b) Motion of a toy train on a circular track.
(c) Motion of a racing car on a circular track.
(d) Motion of hours’ hand on the dial of the clock.

3. Which of the following graph represents uniform motion of a moving particle?

Dist

Dista
anc

ance

Distanc
Dist

(a) (b) (c) (d)

nce
e

Time Time Time

[]
18 SURA’S Science - 9th Std Unit 02 MOTION
4. The centrifugal force is
(a) a real force.
(b) the force of reaction of centripetal force.
(c) a virtual force.
(d) directed towards the centre of the circular path.
II. Fill in the blanks :
1. Speed is a _________ quantity whereas velocity is a ________ quantity.
2. The slope of the distance – time graph at any point gives ________.
3. Negative acceleration is called _________.
4. Area under velocity – time graph shows ____________.
III. State whether true or false. If false, correct the statement :
1. The motion of a city bus in a heavy traffic road is an example for uniform motion.

2. Acceleration can get negative value also.

3. Distance covered by a particle never becomes zero but displacement becomes zero.
4. The velocity – time graph of a particle falling freely under gravity would be a
straight line parallel to the x axis.
5. If the velocity – time graph of a particle is a straight line inclined to X-axis
then its displacement – time graph will be a straight line.
IV. Assertion and reason type questions :
Mark the correct choice as:
(a) If both assertion and reason are true and reason is the correct
explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct
explanation of assertion.
(c) If assertion is true but reason is false.
(d) If assertion is false but reason is true.
1. Assertion : The accelerated motion of an object may be due to change in magnitude
of velocity or direction or both of them..
Reason : Acceleration can be produced only by change in magnitude of the
velocity. It does not depend the direction.

2. Assertion : The Speedometer of a car or a motor-cycle measures its average speed.

Reason : Average velocity is equal to total displacement divided by total time
taken. []

3. Assertion : Displacement of a body may be zero when distance travelled by it is

not zero.
Reason : The displacement is the shortest distance between initial and
final position.
 SURA’S Physics - 9th Std Unit 02 MOTION 19

[]
V. Match the Following :
List I List II
1. Motion of a body covering equal
distances in equal intervals of time
O
Time
A Velocity

2. Motion with non uniform acceleration

B Velocity
Time

3. Constant retardation

Velo
city
C
Time

4. Uniform acceleration

ocit
Vel
D

y
Time

VI. Answer briefly :

Define velocity.
1. Distinguish distance and displacement.
2. What do you mean by uniform motion?
3. Compare speed and velocity.
5. What do you understand about negative acceleration?
6. Is the uniform circular motion accelerated? Give reasons for your answer.
7. What is meant by uniform circular motion? Give two examples of uniform
circular motion.

8. Derive the equations of motion by graphical method.

 20 SURA’S  Science - 9th Std Unit 02 MOTION

1. Derive the equations of motion by graphical method. [QY - 2019]

2. Explain different types of motion.
Ans. Different types of motion :
(i) Linear motion : The motion of an object along a straight line is known as
linear motion. Ex : Car moving on a straight road.
(ii) Circular motion : The motion of an object is a circular path is known as circular
motion. Ex : Earth revolving around the sun.
(iii) Oscillatory motion : Repetitive to and fro motion of an object at regular
interval of time is called as oscillatory motion. Ex : Motion of pendulum of a
clock.
(iv) Random motion : The disordered or irregular motion of a body is called
random motion. Ex : Movement of fish under water.

VIII. Exercise Problems :

1. A ball is gently dropped from a height of 20 m. If its velocity increases
–2
uniformly at the rate of 10ms , with what velocity will it strike the ground?
After what time will it strike the ground?
2. An athlete completes one round of a circular track of diameter 200 m in 40 s. What
will be the distance covered and the displacement at the end of 2 m and 20 s?
–2
3. A racing car has a uniform acceleration of 4ms . What distance it
covers in 10s after the start? INTEXT ACTIVITIES

GOVERNMENT EXAM QUESTIONS

1 MARK

1. Unit of acceleration is [QY - 2019]

–1 –2 2
(a) ms (b) ms (c) ms (d) ms
[]
2. The magnitude of the centripetal force is given by (F = _________)
2 2
(a) MV
(b) V
(c) 2π (d) ma 2

R R T ]
R

3. In India the voltage of alternating current used for domestic purpose is

______.
(a) 50V (b) 5V (c) 220V (d) 110V
[]
2 MARK
 1. A sound is heard 5 s later than the lightning is seen in the sky on a rainy
day. Find the distance of location of lightning? Given the speed of sound
–1
= 346 ms

ADDITIONAL QUESTIONS

I. Choose the correct answer :

1. A particle is moving in a circular pattern of radius r. The displacement after
half a circle would be
(a) zero (b) πr (c) 2r (d) 2πr
2. In which of the following cases of motions, the distance moved and the
magnitude of displacement are equal?
(a) If the car is moving in the straight road.
(b) If the car is moving in a circular road.
(c) The Earth is revolving around the sun.
(d) The pendulum is moving to and fro
3. A body is thrown vertically upward with velocity u, the greatest height h to
which it will rise is
2 2
(a) u /2g (b) u /g (c) u/g (d) u/2g
4. If the displacement of an object is proportional to square of time, then the
object moves with
(a) uniform velocity (b) uniform acceleration
(c) increasing acceleration (d) decreasing acceleration
5. From the given v–t graph, u can be inferred that the object is

Velocity
(a) in uniform motion (b) at rest Time
(c) in non-uniform motion (d) moving with uniform acceleration
6. Area under v–t graph represents a physical quantity which has the unit.
2 3 –1
(a) m (b) m (c) m (d) ms
2
7. m/s is the unit of
(a) distance (b) displacement (c) velocity (d) acceleration
8. The rate of change of displacement
(a) speed (b) velocity (c) acceleration (d) retardation
]
9. A scalar quantity has
(a) magnitude only (b) direction only
(c) both (d) none []
10. When an object undergoes acceleration
(b) there is always an increase in its speed
(c) a force always acting on it.
(d) all of the above ]
 SURA’S Physics - 9th Std Unit 02 MOTION 27

11. A body is projected up with an initial velocity u m/s. It goes up to a height, ‘h’
metres in ‘t’ seconds time. Then it comes back at the point of projection.
Considering negligible air resistance, which of the following statement is true?
(a) the acceleration is zero
(b) the displacement is zero
(c) the average velocity is 2h/t
(d) the final velocity is 2u when body reaches projection point
2
12. A car accelerates at 1.5m/s in a straight road. How much is the increase in
velocity in 4s.
(a) 6 m/s (b) 4 m/s (c) 3 m/s (d) 2.66 m/s
13. The slope of the distance time curve is steeper / greater is the _________
(a) velocity (b) acceleration (c) displacement (d) speed
14. The given graph represents motion with ________ speed.

Distance
(a) uniform (b) non uniform
(c) constant (d) none Time

15. The relation between displacement and time is given by the equation of
2 2 2 2
(a) v = ut + at (b) s = ut + ½at (c) v = s/t (d) v = u + 2as
16. A body moves in a uniform circular motion
(a) It is moving with constant velocity
(b) its acceleration is zero
(c) the body has an acceleration
(d) none of the above
17. Speed of the body in particular direction can be called
(a) acceleration (b) displacement
(c) velocity (d) distance
18. Statement A : Uniform circular motion is a case of accelerated motion
Statement B : In third equation of motion we do not have the term time
(a) Statement B is true, A is false (b) Statement A is true, B is false
(c) neither statement A nor B is true (d) both are true
19. Which of the following is correct about uniform circular motion
(i) direction of motion is continuously changed
(ii) direction of motion is not changed
(iii) speed and direction both remain constant
(iv) speed is constant but direction is changing
(c) i & iv are correct (d) all of these

20. Which of the quantities have the same SI unit?

(a) speed, velocity (b) acceleration, time
(c) velocity, time (d) velocity, acceleration
21. Rest and motion of body are
(a) non relative (b) not related (c) relative (d) none
 SURA’S Science - 9th Std Unit 02 MOTION
21. Which of the quantities have the same SI unit?
(a) speed, velocity (b) acceleration, time
(c) velocity, time (d) velocity, acceleration
22. Rest and motion of body are
(a) non relative (b) not related (c) relative (d) none
22. An ant moves from one corner of a room diagonally to the opposite corner. If
the dimensions of the hall are 8m × 6m, the displacement of the ant is
(a) 10m (b) 14m (c) 28m (d) 2m
23. The displacement covered by a second hand of radius 'r' in a clock after one
revolution is
(a) 360 (b) 0 (c) 3r (d) 2r

24. A man leaves his house at 6.30 a.m. for a morning walk and returns back at
7.30 a.m. after covering 4 km. Displacement covered by him is _________.
(a) 2 km (b) zero (c) 8 km (d) 4 km
25. A body is said to be in non uniform motion if it travels
(a) equal distance in unequal interval of time
(b) equal distance in equal interval of time
(c) unequal distance in unequal interval of time
(d) unequal distance in equal interval of time.
26. A quantity which has both magnitude and direction is
(a) scalar (b) distance (c) vector (d) moving body
–2 –1
27. A bus accelerating with 4ms changes its speed from 60ms to a certain
value in 5s. The final speed is
(a) 40 m/s (b) 25 ms–1 (c) 60 ms–1–2 (d) 30 ms–1
28. A quantity has a value of –16ms . It is the
(a) acceleration of an object (b) velocity of an object
(c) retardation of an object (d) speed of an object

29. A boy throws a ball up and catches it when the ball falls back. In
which part of the motion the ball is accelerating?
(a) during downward motion (b) when the ball comes to rest
(c) during upward motion (d) when the boy catches the ball.

30. Choose the correct option.

(a) distance is a scalar, velocity is a vector, acceleration is a vector

(c) distance is a vector, velocity is a vector, acceleration is a vector

distance is a scalar, velocity is a vector, acceleration is scalar
31. If a moving body comes to rest, then its acceleration is

(a) positive (b) negative

(c) zero
(d) all of these depending upon initial velocity.
 32. If the velocity of a body changes uniformly from u to v in time t, the sum of
average velocity and acceleration is
(a) (U+V) (b) (V−U) (c) 2U (d) 2V
T T T T

33. Acceleration is defined as the rate of change of

(a) distance (b) velocity (c) speed (d) displacement

34. When an object undergoes acceleration

(a) there is always an increase in its velocity
(b) there is always an increase in its speed
(c) a force always acting on it.
(d) all the above

35. The equation v = u + at gives information as

(a) velocity is a function of time
(b) velocity is a function of position
(c) position is a function of time
(d) position is a function of time and velocity

36. Which of the following can determine the acceleration of a moving object.
(a) area of velocity time graph (b) slope of velocity time graph
(c) area of distance time graph (d) slope of distance time graph

37. What is the slope of the body when it moves with uniform velocity?
(a) positive (b) negative (c) zero (d) may be positive or negative

38. If a body starts from rest, what can be said about the acceleration of body?
(a) positively accelerated (b) negative accelerated
(c) uniform accelerated (d) none of the above

39. When a body moves uniformly along the circle then

(a) its velocity changes but speed remains the same
(b) its speed changes but velocity remains the same
(c) both speed and velocity changes
(d) both speed and velocity remains same

40. Distance travelled by a freely falling body is proportional to

(b) square of the acceleration due to gravity
(c) square of the time of fall
(d) time of fall

41. If the displacement - time graph of a particle is parallel to the time axis, then
velocity of the particle is.
(a) infinity (b) unity (c) equal to acceleration (d) zero
30 SURA’S Science - 9th Std Unit 02 MOTION

42. In the velocity time graph, AB shows that the body has
(a) uniform acceleration
(c) uniform speed
A
(b) non-uniform retardation
B

O
(d) initial velocity OA & is moving with uniform retardation. Time
–1 –2
43. A body moving with an initial velocity 5ms and accelerates at 2ms . Its
velocity after 10s is
–1 –1 –1 –1
(a) 20ms (b) 25ms (c) 5ms (d) 22.55ms
44. In a 100m race, the winner takes 10s to reach the finishing point. The average
speed of the winner is
–1 –1 –1 –1
(a) 5ms b) 20ms c) 40ms d) 10ms
45. The area under velocity – time graph represents
(a) velocity of the moving object
(b) displacement covered by the moving object
(c) speed of the moving object
(d) acceleration of the moving object
–1
46. A car is being driven at a speed of 20ms when brakes are applied to bring it
to rest in 5 s. The deceleration produced in this case will be
–2 –2 –2 –2
(a) +4ms (b) –4ms (c) –0.25ms (d) +0.25ms
47. The force responsible for drying of clothes in a washing machine is ________.
(a) Centripetal force (b) Centrifugal force
(c) Gravitational force (d) Electro static force

II. Fill in the blanks :

1. If a body does not change its position, then it is said to be at _____.
2. The back and forth motion of a swing is an _____ motion. []
3. In uniform motion an object travels equal _____ in _____ interval of time.
]
5. Displacement is the _____ distance covered by a body. ]
6. The motion of the bus is _____ motion. ]

7. Rate of change of displacement is _____.

8. Speed is a _____ quantity whereas velocity is a _____.
9. If final velocity is less than initial velocity the acceleration is _____.
10. If final velocity is equal to initial velocity the value of acceleration is _____.
11. The slope of distance time graph becomes steeper & steeper the speed ______.
12. A straight line parallel to x-axis in velocity time graph, it represents the
object moves in _______. [
13. From v–t graph _______ can be calculated.
14. ______ measures the instantaneous speed of the automobile.
15. Slope of velocity time graph gives ________.
 SURA’S Physics - 9th Std Unit 02 MOTION 31
16. The value of acceleration for a body at rest is ________.
17. At the highest pount, when a body is thrown vertically upwards, the velocity is _____.
18. A body moves in a circular pattern the _____ of velocity does not change but _____
changes.
19. When a body moves in a circular pattern _____ acceleration is directed radially towards
the centre of the circle.
20. The separation of cream from milk an example for the application of _____.
21. Consider an object is rest at position x = 20m. Then its displacement – time graph
will be straight line _____________ to the time axis.
III. State whether true or false. If false, correct the statement :
1. Displacement can be zero but distance never.
2. Time is a vector quantity.
3. Displacement magnitude can be grater than distance travelled by the object.
4. If the velocity of the body decreases with time the acceleration is negative and
the motion is called decelerated motion.
5. Acceleration is a scalar.
6. The area of the velocity time graph gives displacement of the body.
7. Motion & rest are relative terms.
8. An object can be moving with uniform speed but variable acceleration.
9. Slope of distance-time graph indicates the speed.
10. It is possible to have object moving with uniform velocity but non-uniform acceleration.
11. It is possible to have object moving with uniform speed but variable acceleration.
12. The force experienced by a boy in the merry-go-round is a centripetal force.
13. The initial velocity of a freely falling object is zero as it is released from rest.
14. The initial velocity of a freely falling object is zero as it is released from rest.

IV. Assertion and reason type questions :

(a) If both assertion & reason are true and the reason is the correct
explanation of the assertion.
(b) If both assertion & reason are true but the reason is not correct
explanation of the assertion.
(c) If assertion is true but reason is false.
(d) If assertion & reason both are false.
(e) If assertion is false but reason is true.
32 SURA’S Science - 9th Std Unit 02 MOTION

1. Assertion : A body can have acceleration even if its velocity is zero at a given
instant of time.
Reason : A body is momentality at rest when it reverses its direction of motion.
2. Assertion : If the displacement of the body is zero, the distance covered by it may
not be zero.
Reason : Displacement is a vector & distance is a scalar quantity.
3. Assertion : An object can have constant speed but variable velocity.
Reason : Speed is a scalar but velocity is vector.
4. Assertion : The speed of a body can be Negative.
Reason : If the body is moving in the opposite direction of positive motion,
then its speed is Negative.
5. Assertion : The position - time graph of a uniform motion in one dimension of a

Reason : When the speed of body decreases with time then, position-time
graph of the moving body has Negative slope.

6Assertion : A positive acceleration of a body can be associated with slowing down

of the body.
Reason : Acceleration is a vector.
7Assertion : A negative acceleration of a body can be associated with speeding up
of the body.
Reason : Increase in speed of a moving body is independent of its direction of
motion.
8Assertion : When a body is subjected to an uniform acceleration, it is always move
in a straight line.
Reason : Motion may be straight line motion or circular motion.

9Assertion : Position-time graph of a stationary object is a straight line parallel to

time axis.
Reason : For a stationary object, position does not change with time.
10. Assertion : The slope of distance-time graph of a body moving with high speed is
steeper than slope of distance -time graph of a body with low velocity.
Reason : Slope of distance-time graph = speed of the body.

V. Answer briefly :
1. What is centripetal acceleration and centripetal force?
Ans. When a body moves in a circular pattern the acceleration is directed
radially towards the centre of the circle.
The force causing this acceleration is also directed towards the centre of
the circle and it is called centripetal force.
SURA’S Physics - 9th Std Unit 02 MOTION 33
V. Answer briefly :

2. Find the magnitude of centripetal force.

Ans. Consider an object of mass m, moving along a circular path of radius r, with a
velocity v, its centripetal acceleration is given by
2
a = v /r
Hence, the magnitude of centripetal force is given by,
F = mass × centripetal acceleration
2
F = mv / r
3. What is centrifugal force? Give examples.

force. Thus centrifugal force is in a direction opposite to the direction of centripetal

force. Its magnitude is same as that of centripetal force.
Example : Spin dryer of a washing machine, ride on a merry-go-round.
 4. When an object is thrown upwards, what is true of velocity and acceleration at the
highest point of motion of the object?
5. Name the two quantities, the slope of whose graph gives (i) speed (ii)
acceleration.
6. Define Average speed.

7. What do you infer if

(i) Distance - time graph is straight line.
(ii) Velocity time graph is curved.
(iii) Displacement time is zig zag.
8. Give the formula for each.
(i) Relation between initial, final velocity, acceleration and displacement in a uniformly
accelerated straight line motion.
(ii) Relation between initial, final velocity, acceleration & time in a uniformly
accelerated straight line motion.
(iii) Relation between initial velocity, acceleration, displacement and time.
9. What is the difference between uniform acceleration and non - uniform
acceleration?
 VI. Paragraph Questions :
1.Define acceleration and state its SI unit for motion along a straight line, when do
we consider the acceleration to be (i) positive (ii) negative? Give an example of a
body in uniform acceleration.
2. Distinguish between uniform motion and non uniform motion. Define uniform
circular motion and give example of it. Why is it called accelerated motion?
3. Define uniform circular motion and give example of it. Why is it called accelerated
motion?

4. When a body is said to be in (i) uniform acceleration (ii) non - uniform acceleration?
5. When a body is said to be in (i) uniform acceleration (ii) non - uniform acceleration?
6. What remains constant in uniform circular motion? And what changes continuously in
uniform circular motion?

7. What remains constant in uniform circular motion? And what changes continuously in
uniform circular motion?

PROBLEMS

1. A bus speed decreases from 50 km/h to 40 km/h in 3s, find the acceleration of the
bus.
–2
2. A car starting from rest moves with uniform acceleration of 0.2 ms for 3 min.
Fine the (a) speed acquired (b) the distance travelled.
–1
3. A train is travelling at a speed of 90 kmh . Brakes are applied so as to produce
–2
a uniform acceleration of –0.5 ms , find how far the train will go before it is
\ brought to rest.

4. In a long distance race the athletes were expected to take four rounds of the track such
that the line of finish was same as the line of start. Suppose the length of the
track was 300m, C 7. In a
(i) What is the total distance to be covered by the distanc
athletes? e-
(ii) What is the total displacement of the athletes when time
they touch the finish line? graph
of two
(iii) Is the motion of the athletes uniform or non- objects
uniform? D
A&
(iv) Is the displacement & distance moved by athlete
aT the end of the race equal?

5. Ram swims in a 80m long swimming pool. He covers

160m in 1 min by swimming from one end to the other
and back along the same straight pattern. Find the
average speed and average velocity.
6. A bus from Chennai travels to Trichy passes 100 km, 160
km at 10.15 am, 11.15 am respectively. Find the average
speed of the bus during 10.15 - 11.15 am.
 B, which object is moving with greater speed when both are B

moving?
300
8. Find the distance covered by a particle during the time interval t =
0 to t = 20s for which the speed - time graph is shown in figure.

9. A car moves 30 km in 30 min and the next 30

km in 40 min. Calculate the average speed for
the entire journey.
 10. A boy travels a distance of 3m due east and then 4m due north.
(a) How much is the total distance covered?
(b) What is the magnitude of the displacement?

11. During an experiment, a signal from a spaceship reached the ground station in five
seconds. What was the distance of the spaceship from the ground station?
8 -1
The signal travels at the speed of light that is 3 × 10 ms .

12. A train travelling at a speed of 90kmph. Brakes are applied so as to

–2
produce a uniform acceleration of –0.5 ms . Find how far the train will
go before it is brought to rest?

13. The adjacent diagram shows the velocity time graph of a body.
a) During what time interval is the motion of the body accelerated?
b) Find the acceleration in the time interval mentioned in part ‘a’.
c) What is the distance travelled by the body in the time interval mentioned in part ‘a’?

14. The following graph shows the motion of a car. What do you infer from the
graph along OA and AB? What is the speed of the car along AB and
what time it reached this speed.
a) What do you infer from the graph along OA and AB
b) What is the speed of the car along AB?
c) What time it reached this speed.

15. From the following table, check the shape of the graph.
Time (s) 0 2 4 6 8 10 12
–1
Velocity (ms ) 0 20 40 40 40 20 0

……………………………….