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Chapter 3
Motion
(Every action has reaction! Yes exactly, if you do not please your books how will you
be pleased…?)
 Definitions:
1. Motion: - When an object changes its position with respect to its surrounding it
is said to be in motion.
2. Rest: - When an object does not change its position with respect to its
surrounding it is said to be at rest.
3. Translatory (or linear) motion: - A body is said to possess translatory motion
when it follows straight path.
4. Rotatory (or circular/angular) motion: - When a body moves in a circle (i.e.
may spin or rotate about a fixed point).
5. Oscillatory (or vibratory) motion: -when a body moves to and fro about its
mean position
6. Kinematics: - It is the study of motion of objects without considering the forces
acting on them
7. Statics: - The study of objects at rest
8. Dynamics: - It is the study of cause of motion.
9. Rate: - Anything divided by time.
10. Displacement: - the shortest straight distance between the two points, having a
particular direction. Or the change in position of the body.
11. Distance: - it is the length of the path (curved/line) described by an object
moving in space.
12. Velocity: - the rate of change of displacement is called velocity

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13. Uniform velocity: - The velocity which does not change in magnitude and
direction. OR. It is the equal distance covered by a body in equal intervals of
time in particular direction
14. Speed: - the magnitude of velocity is called speed. OR the rate of change of
distance is called speed.
15. Acceleration: - the rate of change of velocity is called acceleration.
16. Uniform acceleration: - when the change in velocity is constant in equal
intervals of time.
17. Gravity: - It is the force by virtue of which the earth attracts the bodies towards
its centre.
18. Acceleration due to gravity: - It is the acceleration in free fall bodies by
gravity.
19. Newton’s First Law of Motion: - it states that
“A body continues its state of rest or uniform motion unless an external
force acts on it”
20. Inertia: -It is the property of matter by virtue of which it opposes any change in
its state of rest or that of motion.
21. Force: -It is the agency that causes or tries to change the state of rest or that of
the motion of the body.
22. Newton’s second law of motion: - According to it
“When an unbalanced force acts on a body it produces acceleration in the
body in the direction of force which is directly proportional to the force and
indirectly proportional to mass of the body”
23. Newton’s third law of motion: - It states that
“Every action has an equal and opposite reaction”
24. Weight: - Weight of the body is the gravitational pull of the earth on the body.

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25. Tension: -When an object is suspended by a string the force that acts along the
string and is equal in magnitude and opposite in direction to the weight is called
tension.
26. Thrust: -A forcefully pushing force.
27. Up thrust: - It is the force that pushes things up in water.
28. Reaction: -The opposing force of action (which is the application of force)
29. Friction: -The resistive or opposing force to the motion of the object generated
when the two surfaces or in contact.
30. Static Friction: -The friction between the body and the surface when the body
is at rest
31. Kinetic or dynamic Friction: -When the body is in motion relative to the
surface then the force of friction between the object and surface is of dynamic
type.
32. Sliding Friction: -When a body slides on a surface the corresponding force of
friction is called sliding friction.
33. Rolling Friction: -When a body rolls on a surface the corresponding force of
friction is called rolling friction.
34. Limiting Friction: -The maximum static friction when the object is on the
verge of slipping is called limiting friction.
35. Fluid Friction: -When a solid object moves through a fluid (viscous medium),
it experience an opposing force on it, called fluid friction.
36. Resistance: -the force that prevents the motion.
37. Frame of Reference: -A set of coordinate axes in terms of which the position
or movement may be specified or with reference to which physical phenomenon
may be stated mathematically.

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38. Internal frame of reference: -A frame of reference which is at rest or moves
with constant velocity and the acceleration in it is zero, also it allows the
Newton’s law to be applicable it.
39. Non inertial frame of reference: - Such a frame of reference is accelerated.
40. Momentum: - It is defined as the product of mass and velocity of the body.
41. Law of conservation of momentum: -The total momentum of an isolated
system before and after collision remains conserved.
42. Impulse: -The change in momentum that takes place when a large force acts for
a short interval of time.
43. Elastic collision: - The collision after which both the momentum and kinetic
energies are conserved.
44. Inelastic collision: -In such a collision momentum is conserved but the kinetic
energy is altered.

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 Scientific Reasons:
Q 1. Why it is easier to stop a bicycle than a truck moving with the same
velocity?
Ans. Because the bicycle has small momentum due to its small mass as
compared to the truk
Q 4. Will a body accelerate more at the same time when you increase its
mass? Explain.
Ans. No, because according to Newton’s 2nd
law of motion acceleration is
directly proportional to force but at the same time indirectly proportional to
mass.
Q 2. Why the same bullet thrown with the hand does not harm so much as
fired from gun?
Ans. Because the bullet thrown with hand has small momentum because of its
low
Velocity as compared to the bullet fired from gun.
Q 3. Why the gun recoils on firing?
Ans. This phenomenon is in accordance with Newton’s third law of motion in
which The action of firing of bullet produces the reaction of recoiling of
gun.
Q 4. Why the leaves fall off on jerking the tree?
Ans. They fall off due to inertia. When you jerk tree the leaves are set on
motion which on the stoppage of jerking still want to be in motion with high
amplitude which cause them to fall off. This is a case of Newton’s first law
of motion.
Q. 5 Why one has to run a while during stepping out of a moving vehicle?
Ans. It is because of inertia. When a person steps out of a moving vehicle his
feet come to rest but his rest of the body is still in motion which will cause
him to fall on the ground. In order to save from falling on the ground one
should run for a while after stepping out of a moving vehicle.

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Q. 6 Will the momentum be conserved after collision of balls in snooker
game?
Ans. No, because it is not an isolated system and due to friction the
momentum could not remain conserved.
Q. 7 Jelly fish pushes water out of its mouth backward and is its propelled
forward. Explain the phenomenon.
Ans. it is according to Newton’s third law of motion. The pushing of water
out of mouth in backward direction is action whose equal and opposite
reaction is displayed by the forward movement of jelly fish.
Q. 8 Can a body with moving constant speed has acceleration? Explain.
Ans. yes, because acceleration is produced as a result of change in velocity
and speed + direction constitute velocity. So, the change in any of the speed
or direction will cause acceleration as is the case seen in the motion along
circle.
Q. 9 Does a body with uniform acceleration has constant velocity? Explain.
Ans. No, because acceleration is the rate of change of velocity and a body
with constant velocity cannot be accelerated even uniformly.
Q. 10Why the front of vehicles is made inclined or slanted?
Ans. It is designated so in order to bear less frictional resistance offered
by the wind.

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 Multiple Choice Questions
1. Momentum =
a) mass × velocity b) mass × acceleration
c) force × velocity d) force × acceleration
2. Find the incorrect statement about force:
a) its S.I unit is Newton
b) it always produces motion
c) force and acceleration are directly proportional to each other
d) F=ma
 Questions 3 - 10
 Select from the terms below
A) Newton’s first law of motion
B) Newton’s second law of motion
C) Newton’s third law of motion
D) N.O.T
3. Every action has an equal and opposite reaction is the statement of:
4. Also known as law of inertia
5. Acceleration is directly proportional to force is the statement of:
6. Walking and firing of bullets are the examples of:
7. Acceleration is directly proportional to mass is the statement of:
8. Motion of boat obeys:
9. The flight of birds shown by the upward and downward motion of their wings is
in accordance with:
10.Falling of leaves from plants on jerking is in accordance with:

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1 A 2 B 3 C
4 A 5 B 6 C
7 D 8 C 9 C
10 A
11. Far walking it is not necessary:
a) friction b) gravity
c) smoothness d) N.O.T
12. The unit of momentum is:
a) N b) N.m
c) Nm-
d) Nm-2
13. The maximum force of friction which just stops body from sliding or moving is called:
a) rolling friction b) static friction
c) kinetic friction d) limiting friction
14. When force acting on a body is doubled its acceleration becomes:
a) ½ b) ¼
c) doubled d) quadrupled
15. Find the force acting on a body of mass 10kg moving with the acceleration of 5m/s2
.
a) 5N b) 15N
c) 30N d) 50N
16. What is mass of a body of weight 9.8N
a) 1kg b) 1g
c) 9.8kg d) 9.8g
17. How much acceleration will be produced in a body of 15kg if force of 30N acts on it?
a) 1m/s2
b) 2m/s2
c) 3 m/s2
d) 3 m/s2
18. What is the mass of a body if the force of 20N produces acceleration of 5 m/s2
a) 3kg b) 4kg
c) 15kg d) 400g
19. What is the weight of a body of mass 10kg
a) 10N b) 19.6N
c) 49N d) 98N
20. A stone weighing 2N is placed over wooden table. The friction between stone and the table
is:
a) 0.08N b) 0.8N
c) 8N d) N.O.T

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11 C 12 B 13 D
14 C 15 D 16 A
17 B 18 B 19 D
20 B
21.A force of 54N acts on a stationary body for 2s and the body acquires velocity
of 18m/s. the mass of body is:
a) 6kg b) 8kg
c) 18kg d) 32kg
22.A body weighing 19.6N is resting at a place. What force is needed to produce
acceleration of 2 m/s2
a) 2N b) 4N
c) 9.8N d) 39.2N
 Questions 23-35
 Select from the terms below
A) True B) False
23.Mass and weight both have same unit
24.The weight of a body is always constant
25. m1v1 + m2v2 = m1u1 + m2u2 represents law of conservation of momentum
26.Weight is a scalar quantity
27.Friction is directly proportional to deceleration
28.Friction will not be produced if the two surfaces in contact are totally smooth.
29.Rolling friction is lesser than sliding friction
30.It is always necessary to apply force to stop moving object

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21 A 22 B 23 B
24 B 25 B 26 B
27 B 28 A 29 A
30 A
31.The quality of matter of a body is called its mass
32.Action and reactions have equal magnitude but different direction
33.When an unbalanced force acts on a body it always produces acceleration
34.The friction during motion is called kinetic motion
35.It is dangerous to jump from moving train because of inertia.
36.A body of mass 10 Kg attains the velocity of 10m/s within 10s. the force acting
on it is?
a) 1 N b) 10N c) 100N d) N.O.T
37.A car is moving with the velocity of 36km/h on a straight road. On applications
of brakes it comes to rest after covering a distance of 5m. the deceleration
produced is:
a) 5m/s2
b) -5 m/s2
c) 10 m/s2
d) -10 m/s2
38.A ball is dropped from tower. It reaches the ground in 5s. The velocity with
which it strikes the ground is:
a) 9.8m/s b) 19.4m/s
c) 49m/s d) 98m/s
39.The two balls ball A and ball B of masses 50g and 100g respectively are
dropped from a tower. The correct statement is:
a) ball A will reach the ground first
b) ball B will reach the ground first
c) both the balls will reach the ground simultaneously
d) the balls don’t have acceleration

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40.An athlete running with the speed of 10m/s reaches its target within 5min. Find
the distance traveled by the athlete.
a) 1km b) 2km
c) 3km d) 500m
41.A body starts from the rest and attains the uniform acceleration of 10 m/s2
within 3s. find the distance covered.
a) 7m b) 16m
c) 30m d) 45m
31 B 32 A 33 A
34 A 35 A 36 B
37 D 38 C 39 C
40 C 41 D 42
42.A body has velocity of 5m/s and increasing up to 10m/s within 2.5s. the
acceleration produced is:
a) 1 m/s2
b) 2 m/s2
c) 3 m/s2
d) 4 m/s2
43.A body starts from rest and attains the velocity of 2m/s within 1s. Find the
distance covered while its acceleration is 2 m/s2
a) 1m b) 2m
c) 3m d) 4m
44.A car starts from rest and attains velocity of 90m/s within 1min. its acceleration
is:
a) 1 m/s2
b) 1.5 m/s2
c) 2 m/s2
d) 90 m/s2
45.An object falling freely under gravity has constant velocity:
a) true b) false
46.what is speed of a body if it covers 10m/s within 2s
a) 5m/s b) 10m/s
c) 15m/s d) 20m/s

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47.A batsman hits the ball with the initial velocity of 30 m/s and it attains the
uniform acceleration of 10m/s2
within 2s. The distance covered is:
a) 20m b) 40m
c) 60m d) 80m
48.What will be the final velocity of a ball dropped from the top of building which
attains the acceleration of 9.8m/s2
and takes 4s to reach the ground?
a) 4.9m/s b) 19.6m/s
c) 39.2m/s d) N.O.T
49.A ball is thrown with the velocity of 6m/s and it attains the acceleration of
4m/s2
. What will be its velocity after 2s.
a) 4m/s b) 6m/s
c) 10m/s d) 14m/s
50.A body starts from the rest and attains the uniform acceleration of 8m/s2
within
3s. find the distance covered.
a) 8m b) 16m
c) 24m d) 36m
42 B 43 A 44 B
45 B 46 B 47 D
48 C 49 D 50 D
51.A body moving towards north with the speed of 50m/s turns to east and its
speed becomes 60m/s. the acceleration produced is due to change in _______of
velocity.
a) magnitude b) direction
c) both a & b d) N.O.T
52.If a body moves with uniform acceleration its velocity doesn’t change.
a) true b) false
53.acceleration is always produced when there is change in the speed of a body:
a) true b) false
54.A body has the velocity of 2m/s in the 1st
second, 4m/s in the 2nd
and 3m/s in
the 3rd
second. The average velocity is:

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a) 2m/s b) 3m/s
c) 4m/s d) 5m/s
55.A car starts from rest and attains velocity of 16m/s within 4s. its acceleration is:
a) 4 m/s2
b) 12 m/s2
c) 20 m/s2
d) 64 m/s2
56.A book kept in a moving car is in rest according to the passengers in the car:
a) true b) false
57.What is the speed of a bullet if it takes 4 s to hit its target at 4 km?
a) 400 m/s b) 500 m/s
c) 1000 m/s d) 2000 m/s
58.A body moving with the constant speed of 10m/s changes its direction from
north to east after some time. The body is said to be accelerated.
a) true b) false
59.1 nm = 109
km
a) true b) false
60.What is the acceleration of a body moving with the constant velocity of 12m/s
and reaches its target within 3s.
a) 36 b) 3
c) 4 d) N.O.T
51 C 52 B 53 A
54 B 55 A 56 A
57 C 58 A 59 B
60 D

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