SYNOPSIS 6

Apparent Weight:
A person with mass m who is located at or near the surface of the Earth will
always have some weight W mg. When a person
=
stands on a scale, the reading
on the scale is
actually the normal force that the
scale exerts back towards the
person to support the person's weight. (Note that the person and the scale are
stationary relative to each other, in other words they are always in contact with
each other, so
they always have equal and opposite action and reaction forces
acting between them.)
Things get complicated, though, when the scale and the
eration. This will person experience accel-
change the contact force (the Normal Force) between the person
and the scale.

Let's look at several cases. We will

assume that up is the positive direction and
Down is the negative direction.
Case 1: No acceleration of elevator
If the acceleration of the elevator
is zero, then there two
the elevator can be at rest possible scenario;
are
(stationary, zero velocity) moving with a constant
or
speed (no acceleration if velocity does not change).
In this case, the action and reaction force
is just the weight. The
pair between the person and the scale
person pushes down onthe scale with a force of
-W=-mg (negative direction) and the scale pushes back up against the man with
a Normal Force of Fy +W +mg. Because the
reading on the scale is the magni-
= =

tude of the normal force. the scale will read the true
NOT accelerating.
weight when the elevator is

person

W=mg

Case 2: going up & speeding up (acceleration a is

positive (up)
In this case, the elevator and the person are starting from rest at
a lower floor.
The elevator accelerates upward. The inertia of the person would
prefer to stav
stationary so the elevator floor and scale must push up on the person to acceler-
atehim upward along with the elevator. (The person doesnt sink into the
floor
when the elevator accelerates up. The elevator ana tne scale and the person
all
move together).
 l a s s w o K DOOR

The
scale therefore has to push upward with extra force on the
ate person to acceler
the person's mass upward. This result in a greater contact force
Scale arnd the between the
person. Therefore the Normal Force is
scale is a number that is
larger, so the reading on the
GREATER than the true weight.

personn a

W-mg

Let us consider Newton's 2nd Law (2F= ma) acting on the

person. The overall
acceleration of the person is upward (with the
elevator). So ma is positive (up-
ward). The only external forces acting on the person and the force of gravity acting

down (-W=-mg) and the supporting. Normal Force F, that the scale applies

upward on the person. So 2F =ma=-mg + F We want to know Fy because that

is the number that we read off the scale. Fy = mg + ma, which is GREATER than

the true weight.

Case 3: going up & slowing down (acceleration a is negative (down))
In this case, the elevator and the person are initially moving upward at a constant
speed and slowing down to rest at a higher floor. The acceleration of the elevator
is downward (opposite to the person which causes a reduction of the velocity). The
inertia of the person would prefer to keep moving upward at constant speed, so
the elevator floor and scale effectively drop out a little bit from underneath the

person a s the elevator

slows down.

person| |a

W-mg
F
again the elevator and the person
move
because
The person doesn't float upward,
the person and the scale is reduced. Th-
but the contact force between
together, with less torce on the person to support th
therefore has to push upward
scale the reading on tha
Therefore the Normal Force is smaller, so
person's weight. the true weight.
that is less than
Scale is a number
The overa_
consider Newton's 2 Law2 ma) acting on the person.
=

Let u s So m a is negativ
is doOwnward (with the elevator).
acceleration of the person
 work Book
VIl-Physics (Vol-IH
down ward). Thc only external forces acting on the person are the 1ore o
Favity
acting down (-W= ma) and the supporting Normal Force F, that the
sCale ap
plies upward on
the person. So 2F=-ma mg + F. We want to know F, because
that is the number
that we rcad off the scale.
the true weight. F, mg ma, which is LESS than

Case 4: going down& slowing down (acceleration

n this case, the
a is positive (up))
elevatorand the person are
Constant speed and then slow to rest initially moving downward at a
at a lower floor. The
upward (opposite direction elevator accelerates
to
nitude). The
inertia of the negative/downward velocity to reduce velocity mag
person would prefer to
constant speed, so the keep
elevator floor and scale must moving on
downward at tne
accelerate him upward, push up the person to
here either Elevator and slowing him down. (The
person doesn't sink into the fl0or
scale and person
move together.)

person a

W=mg
Fs

The scale therefore has to

push upward with extra force on the person to acceler-
ate the person's mass
upward. This results in a greater contact force between the
scale and the person. Therefore the Normal
Force is
scale is a number that is GREATER than the true larger,
so the
reading on the
weight.
Let consider Newton's 2nd Law
us
F= ma)acting on the person. The overall
acceleration of the person is upward (with the
elevator). So ma is
ward). The only external forces acting on the person are the force of positive (up-
gravity acting
down (-W=-mg) and the supporting Normal Force Fy that the scale applies upward
on the person. So F=ma=-mg+FN (Note that this is the same
equation as we

got in case 2.) We want to know Fy because that is the number that we

Case 5: going down & speeding up (acceleration a is negative down)

In this case, the elevator and the person are initially at rest at a higher floor. The
elevator then speeds up in the downward direction towards lower floor. The a
elevator acceleration of the elevator 1s negative/downward
ity magnitude in the downward direction.) The inertia of the
(increasing the veloc-
person would prefer
to stay at rest. So the elevator tloOr and scale etfectively
underneath the person as the elevator accelerates down.
drop out a little bit from

48 Naravana Groun of fahaalsl

 personn

W-mg

F-0
and t h e
again the elevator
there also, because
The peTSOn doesn't float upward 1s
and the scale
force between the person
the contact
person m o v e together, but the person to
with less force o n
reduced. The scale therefore has to push
upward
the read
Normal Force is smaller, so
Therefore the
support the person's weight.
the true weight.
the scale is a number that is LEsS than
ing on

overall
the person. The
on
consider Newton's 2nd Law F=ma)acting
Let us
So m a is negative
acceleration of the person is downward (with the elevator).
force of gravity
acting the person a r e the
on
external forces
(downward). The only
the scale ap-
and the supporting
normal force Fy that
acting down (-W =
-mg)
that this is the
-mg + F (Note
plies upward on the person. So F = -ma =

We want to
that we got for Case 3.)
the equation
equation that this is
same
same ma, which
F
-

read off the scale. mg

=

number that we
because that is the
know F
is LESS than the
true weight.

Case 6: freefall (a=-g)

system would
the whole elevator-scale-person
w e r e to break,
If the elevator cable All objects in freefall1
downward due to the force of gravity.
accelerate
all, begin to s a m e magnitude
(acceleration due to gravity, g).
with the
accelerate downward NO c o n t a c t forcce
a r e freefalling
together, s o there is
The scale and the person a r e both falling
and the person. (When they
between the scale
(Normal Force) of the person's weight.)
that the scale c a n support any
together, there is no way

person a

W=mg
F

which we discussed in
d o w n w a r d acceleration,
case of is
Note that this is a special weight (which zero
Cases 3 a n d 5, the apparent
Just a s in
Case 3 and Case 5. the true weight.
less than
when a--g) is
49
 (CC elun 7t

Oympiad Class Work Book -VIl -Physics (Vol-I1)

A Actorial sumamary of
apparent weight:

3.
a

a = 0
a
ag
Greater than
Normal weight|
Less than
Normal Normal weight|
Weight
Zero weight

WORKSHEET 06
cUQ
You have just boarded the elevator. The elevator, you and the apple are at rest.
What are the torces acting on you?
1) your weight 2) the floor pushing up
3) the loor pushing down 4) both (1) & (2)

2 The elevator with you inside begins to accelerate 2m/s* upwards (take m=50kg).
Tthen calculate the apparent weight of you.
) 490N 2) 590N 3) 690N 4) 390N
3 The elevator with you inside begins to accelerate Im/s* downwards. Then the
appaent weight of you is (take m -50kg)
1) 840N 2) 64ON 3) 240N 4) 440N
The elevator. you and the apple accelerate for 5seconds, at which
time it stops
accelerating and stays at a constant velocity of 10m/s. The acceleration of vou is
1) lm/s 2) 2m/s* 3) 3m/s 4) zero
The elevator cable snaps and the elevator, and the
you elevator, you and the apple
begin to fall in freefall. Your acceleration is

1)9.8m/s* 2) 12m/s* 3) 11.8m/s 4) 7.8m/s*

50
Narayana Groun of fal
 JEE MAIN
LEVEL 1

single Answer Choice Type

lif
man in the lift
1 A 11 novng up with uniform velocity. The apparent weight of the
is
1) More than his true weight 2) Less than his true weight

3) Equal to his true

weight 4) Zero

The apparent weight of a freely falling body is

1) Zero 2) Increased 3) Decreased 4) Constant

3 A lift moving up comes to rest with a retardation. The weight of the man in
it,

1) Increases 2) Decreases
3) Remains constant 4) either increase or decrease

A man weighing 100kg is standing on the platform of stationary lift. The apparent
weight of a man when the lift moves up with an acceleration of 4m/s* is_

(g =10m/s2)
1) 100 kg-wt 2) 140 kg-wt 3) 150 kg-wt 4) 160 kg-wt

JEE MAIN LEVEL 2

5. A body of 1 kg is suspended by string. The tension in thread of the body moves up
with an acceleration of 5m/s2 i s _ 8=10m /s*)
1) 1N 2) 10 N 3) 15 N 4) 20 N
6 A lamp hangs from a light chord from the roof of
elevator when the elevator is
an

descending, it decelerates at 2.5 m /s* before coming to rest. If the tension in

string is 25N, then calculate the mass of the lamp. (g =10m/s*)

1) 1 kg 2) 2 kg 3) 3 kg 4) 4 kg
7. man inside a lift moving up withhas apparent weight W. The same man

inside the lift moving down with an acceleration

ofhas apparent weight W,. Then

the value of W
w, is

1 31 4)
9

arayana Group of Schools 51

 Olympad Clas

LEVEL 3
JEE MAIN
the b i o c k of
so that
be the acceleration 'a' of the box shown
in figure
8. wnat should

mg
mass m exerts a force by the floor on the box?
4

3g
1
3 2)2 3 4) 4

standing there
9 The force exerted by the floor of an elevator o n the feet of a person
is more than the weight of the person, if the elevator is
1) Going up and slowing down 2) Going down and slowing down

3) Going up and speeding up 4) Both (2) and (3)

10. A boy of mass 50kg is standing on weighing machine placed on the floor of a lift.
The machine reads his weight is N. What is the reading of the machine if the lift

of is (Take g = 10ms")
is moving upwards with a uniform speed
1) 510 N 2) 480 N 3) 490 N 4) 500 N

JEE MAIN LEVEL-4

11. A lift is descending with an acceleration of 2m/sec2. What will be the apparent
weight of a person of 80 kg mass?

1) 640 N 2) 472 N 3) 48 N 4) 480 N

12. A man of mass 60 kg is standing on a weighing machine placed on ground. Calcu-

late the reading of machine. (g=10m/s')

1) 640 N 2) 600 N 3) 480 NN 4) 48 N

JEE MAIN LEVEL5

boy whose
13. A
starts to
mass is
ascend with
50kg stands
acceleration
on
a weighing
of the
machine inside a lift. The lift
an reading of the machine or balance
is
1) 60 kg-wt 2) 40 kg-wt 3) 20 kg -wt 4) 80 kg-wt
14. A lift is going up with uniform velocity. When brakees are
applied, it slows down. A
person in that lift experiences

1) More weight 2) Less weight 3) Normal weight 4) Zero weight

52
|Narayana Group of Schools
 Olympiad Class Work BoOR

A man drops an apple in the lift. He finds that the apple remains stationary n i
15
does not fall. The lift is

1) Going down with constant

speed 2) Going up with constant specd

3) Going down with constant acceleration

4) Going up with constant acceleration

The elevator shown in the figure is descending with an acceleration of 2m / s .

16.
The mass of the block A = 0.5kg. The force exerted by the block A on block B

is

A | 2m/S

1) 2 N 2) 4 N 3) 6 N 4) 8 N

JEE ADVANCED LEVEL 1

Comprehension Type:
the floor of an
40kg is standing on a weighing machine kept
on
A man of mass

elevator which is moving up with an acceleration of 2m/s.(g =10ms)

machine is
17. The reading of the weighing

2m/S
3) 88 kg 4) 108 kgg
1) 48 kg 2) 68 kg

with acceleration 2m /s. The reading of th

18
8. An elevator which is moving down
weighing machine is
3) 40 kg 4) 30 kg
1) 45 kg 2) 32 kg
machine is
supporting cable
breaks, the reading of weighing
I f the 4) None
3) 40 kg
1) 1 kg 2) Zero

53
 VVOTR BODn

Matrix Mateh Type:

20 A man of mas m is atanding n aWeigliing maehine plaed in a lifi, TThe wo
forces
acting the the
on man in upwar irelion
Column-I Column-11

a) When the lin in al rest p) N g

b) When the lin is moving upwarda ) N
with an acceleration

c)When the lift is moving downWArds ) N mg

with an acceleration
d) When the lift Ireely
is
lalling ) N-)

SYNOPSIS 7
Friction:

According Newton's first law of motion, a

to
body continues to be in its state of
rest oruniform motion in a straight line unless an
external force act on it. This
means, a ball rolled on the
ground must continue to move forever unless stopped
by some force. Our common exjperience is that a ball rolled on
the ground gradu
ally slows down and finally stops even when no one has
does a rolling ball stopped it. Then, why
stops after moving through a certain distance? The
stops after covering a certain distance due to the force of friction rolling ball
the ball and the acting between
ground. Thus, the force which opposes the relative motion of a
body over the surface of another is called force of friction.
Note:

i) The force of friction is always parallel to the two surfaces.

ii) Normal reaction and frictional force are always perpendicular to each other.
Normal reaction (R):
It is the force acting normal to the
surface of the body in outward
when a body is at rest direction or
on a surface or slides on a
surface, the force exerted by the
surface on the body normal to the surface is known as normal
reaction.
Cause of frietion:
Friction is due to the
irregularities (interlocking) of the two surfaces in contact.
Factors on which frictional force depends:
i) The nature of two surfaces in contact with cach other.

ii) Normal force with the surfaces are being pressed together.
54
 surfaces n
Note: The force of friction does not depend upon the area of the
contact.

Effects of friction:

it moves for a Vnue,

Friction opposes motion: Ifwe roll open a ball on ground
slows down and then stops due to frictional force.

few seconds. They

ii) Friction produces heat: Rub your palms together for a

heat.
become warm. The friction between the palms produces
old shoes anid
Friction causes wear and tear: If we look at the soles
of our
iii) are Worn
compare them with our new pair of shoes we will find that the old ones
and
out. When we walk, the soles wear out due to friction between the ground
automobiles wear out due to friction.
the shoes. Similarly, the tyres of cycles and
Advantages of friction:

together due to friction.

hold the wooden boards
i) Nails and screws

machine by a friction belt.

Power is transmitted from motor to a
ii
to walk on the ground
The friction between our feet and the ground helps us
ii)
without slipping and falling
safe driving.
friction between the road
and the surface of the tyre permits
iv) The
between the pen/
because of the friction
able to write on paper/board
v) We a r e

pencil and the paper. on

able to move
bicycles, cars scooters, etc., are
such as
vi)The moving vehicles and the road surface.
friction between the tyres
the road because of
us from impact of meteors coming from the
friction which saves
of friction be-
vii) It is force of earth's atmosphere, the force
m e t e o r enters
the before reach-
space. When heat such that it burns
a
and air generates enough
tween the m e t e o r
ing ground.
Disadvantages of friction:
Therefore
machines leads to a loss of energy.
various parts of
i) Friction between machines.
reduces the
efficiency of
Inction
machine parts.
and tear of moving
wear
11) Friction causes
c a u s e s dam-
of a machine produces heat and
rotating parts and disadvantages
of friction. It is
ii)Friction between From advantages
is a n evil. evil.
s a m e time it is
friction an
age. Thus and at the
is necessary
clear that friction
evil".
necessary
"Hence friction is a
 Olympiad Class Work Book
= VIl-Physics (Vol- I1)-
Methods of reducing (minimising) the friction:
The friction between two surfaces can be reduced by the following methods.

i) Friction can be reduced by polishing or smoothing the surface.

ii) Friction is reduced in machines by applying oil or grease on the moving parts.

ii) Friction can be reduced by using the ball bearings.

iv) Aeroplanes and automobiles are streamlined in their shape in order to de-
crease air or fluid friction.

Example: Rockets, car, ships, missiles, aeroplanes and automobiles have special
shapes. Birds and fish have streamlined bodies.

Note: Pointed shaped bodies are called streamlined.

v) Friction can be reduced by applying soap solution to the rough surfaces.

vi) Friction can also be reduced by applying powder to the rough surfaces. Graph
ite powder is used in machines to reduce friction.

Example: When a small quantity of powder is applied to the wooden carom board
the surface of carom board becomes smooth and hence the friction between carom
board and coins gets reduced.

Methods of increasing friction:

In certain situations, we need to increase friction, in spite of fact that it con-

sumes more energy. Following examples will illustrate the statement.

i) Tyres of all kinds of vehicles are provided with deep grooves, so as to increase
friction. This prevents the vehicle from skidding on wet roads and sharp turns.

The soles of shoes of athletes and mountaineers are provided with spikes and
grooves. The spikes increase friction and prevent slipping.

ii) Industrial belts are provided with rough surfaces so as to increase friction.
This prevents the belts from slipping over moving iron pulleys.

iv) Soles of our shoes must have grooves.

Types of friction: The force of friction is of three kinds:

1. Static friction

2. Limiting friction

3. Kinetic friction (Dynamic friction)

Kinetic friction is again of two types:

a) Sliding friction and

b) Rolling friction

56
 VIl-Physics (Vol-)- Olympiad Class Work Book
Static iriction (f.): Static friction is the force of friction acting on the body wnen
it is in rest position in spite of the fact that some force is being applied orn .

Note:

1) Fictional force increases with the increase of external force, in case of static
friction.
2) Static frictional force is a self-adjusting force. It can adjust not oniy in
mag
tude but also in direction.

Limiting friction:
The maximum value of the static friction is called limiting friction (or) The maxi
mum frictional force when the body is ready to start is called limiting frictional
force.

fR

Kinetic friction (f):

surface of
The force of friction which opposes when the body in motion on the
the force of
another body or when one body moves over the surface of other,
friction acting between the two surfaces is called kinetic friction.

f R

S =4,R
between two
a) Sliding friction: The force of friction which comes into play
friction.
surfaces, when one tends to slide over the other is called sliding

into play between two

friction: (S) Force of friction which comes
b) Rolling
other is called rolling friction.
surfaces, while one is rolling over

f,oR
S, = u,R

Laws of limiting friction:

direction of motion.
force of friction is always opposite to the
1) The direction of and state of polish of the
friction depends upon the nature
2) The force of limiting
two surfaces in contact.
to the magnitude of
friction T is directly proportional
The mnagnitude of limiting
3) between the two
surfaces in contact, i.e.,
the normal reaction R
= coefficient of friction.
=uR, where jl
fcRorf
between two surfaces is independent of
limiting friction
The magnitude of the a s the normal reaction
re-
4 of the surfaces
in contact as long
the area and shape
mains the same.
57
 i) Coefficient of limiting friction forceof limiting friction
() normal reaction R

Coelficient of kinetic friction forceof kinematic friction. ik

normal reaction R

forceoof rolling
rolling friction
friction f,
ii) Coefficient of rolling friction (,)= 0rce
normal reaction R

f uR =
Lumg (:: R mg)
=

Factors on which coefficient of friction depends:

Coefficient of friction depends on

i) Nature of the surfaces in contact.

ii) It depends on
temperature.

WORKSHEET 07
CUQ
1. Normal reaction acting normal to the surface of the body in_ direction.
1) Inward 2) Outward 3) Parallel to surface 4) None
2. The force of friction is always parallel to the two
1) Objects 2) Forces 3) Surfaces in contact 4) Directions
3 Static friction is a_

1) Self adjust force 2) Parallel force

3) Perpendicular force 4) Both (1) & (2)

4. Generally co-efficient of friction value is

1) Equal to one 2) Less than one 3) Greater than one

4) Zero
5. The magnitude of limiting friction between two surtaces is independent of
the
1) Area of the surface in contact 2) Nature of the surface
3) State of polish of the surface 4) Normal reaction

58
Narnu
 y
Force of friction can.
6.
1) oppose the motion of a body
2) produce heat
31 produce wear and tear
4) all of these
Friction due to of the8e two surfaces in contact.
7.
1) Irregularities 2) Interlocking 3) Either 4) Ncither

The force of friction always acts in this direction

8.
11 parallel to the surfaces in contact
21 perpendicular to the surfaces in contact
3 In the direction of applied forcc
4) All of the above

9.
9. The units of co-efficient of friction is

1) newton
2) newton/sec 3) newton/ sec" 4) no units

JEE MAIN
LEVEL 1
Single Answer Choice Type:
1. The force which opposes the relative motion of a body over the surface another is
called
1) force of friction 2) electrostatic force
3) magnetic force 4) none of these
2 In order to increase friction between two
bodies_
1) their surface of contact should be rough
2) the weight of the body should more
3) both (1) and (2)
4) none of these
3. A good lubricant must be_
1) Highly viscous
2) Low viscous
3) Volatile in nature
4) Highly viscous and low volatile in nature
JEE MAIN
4
f the normal force is doubled, then coetficient of
LEVEL 2
friction is
1) Halved 2) Doubled 3) Not changed
4) Zero
arayana Group of Schools
59
 Olympiad Class Work Book VII-Physics (Vol-I)
5. is a suitable method to decrease friction.

1) ball bearing 2) lubrication 4) all of the above

3) polishing
6. With increase of
temperature, friction
1) Increases 2) Decreases
3) Remains unchanged 4) May increase or decrease

JEE MAIN LEVEL 3

7. The maximum value of static
friction is called
1) Limiting friction 2) Static friction
3) Kinetic friction
4) Rolling friction
8. A force of 100 g-wt is
required to pull a body weighing 1 kg over ice. What is the
co-efficient of friction?g =9.8m
/s
1) 0.01 2) 0.1 3) 1 4) 10.12

JEE MAIN
LEVEL 44
9. Two bodies in contact, but not moving with respect to each other can
exX
ert
1) Static friction on each other 2) Kinetic friction on each other
3) Rolling friction on each other 4) No friction on each other
10. Gymnastic and tennis shoes have rubber soles rather than
leather because
1) rubber sole is lighter than that of a leather
2) rubber sole can be easily washed and cleaned
3) rubber gives better appearance
a

4) rubber provides more friction than leather

JEE MAIN
LEVEL 5
11. A body of mass 5kg moving with a velocity 10ms on a rough horizontal surface is
stopped after a distance of 10m. Then frictional force
acting on it is
1) 25 N 2) 50 N 3) 100 N 4) 200 N
12. A force of 20
kg wt is required to just slide a wooden box
weighing 50 kg over ice.
Then find the coefficient of static friction between the
surfaces in contact is

1) 0.2 2) 0.4 3) 0.8 4) 0.1

60
Naraxann
 Physics (Vol- M)-
Otympiad

JEE ADVANCED LEVEL 1

Statement Type:
13. Statement I: Friction is due to the irregularities of the two surfares in a t

Statement II: Friction is a necessary evil

1) Both Statements are true.

2) Both Statements are false.

3) Statement I is true, Statement II is false.

4) Statement I is false, Statement II is true.

Matrix Match Type:

Column - I
14 Column - I
two surfacesn
a) Disadvantages of friction p) Irregularities of the
contact.

q Wear and tear

b) Advantages of friction
Cause of friction r) Heat production
c)
s) Safe driving
d) Static frictional force
t)Self-adjusting force

15. Co-efficient of friction () =

3) f+R 4) f- R
2) fR
1) f/R

DEE MAIN & ADVANCED LEVEL-2 &a3

Comprehension Type:
friction f is directly proportional to the magnitude of
The magnitude of limiting f
surtaces in contact, i.e..
f
x Ror = uR
between the two
the normal reaction R
=co-efficient of friction).
where, 4

to slide on a rough surface by applying a force

16. 100 g is made just
6. A body of mass

coefficient of friction is (g 10ms)

0.8 N. Then the
3) 0.7 4) 0.6
1) 0.8 2) 0.08
61
 17. A horizontal force of 10 N is necessary to just hold a block stationary against a

wall. The coefficient of friction between the block and the wall is 0.2. The Weight

of the block is_

1) 20 N 2) 50 N 3) 100 N 4) 2 N

18. If 10 N and applied force is 0 N. Then the frictional force acting on the body

is

1) 10 N 2) 5 N 3) 7.5 N 4)ON
19. If , , , are the coefficient of limiting, kinetic, rolling frictions between two

given surfaces arrange them in ascending order?

1) , , H 2) ,,H4 3) 4, , 4) 4 M ,

JEE ADVANCED LEVEL-4&5

Multi Correct Choice Type:

20. Choose the correct statements:

1) Frictional force depends on nature of two surfaces in contact with each other.

2) Frictional force depends on normal force with the surfaces are being pressed
together.

depend upon the area of the surfaces in contact.

3) The force of friction does not

friction depends the area of the surfaces in contact.

4) The force of on

Integer Type:
is made to slide on a rough surface by applying a force of
21. A body of m a s s 100g just

0.4 N. Then the

coefficient of friction is X10". (g =10ms*)

62 Narayana Group of Schools