Romesa’s notes for class matric
CHAPTER NO. 3
PHYSICS NOTES
CLASS MATRIC
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Q: define rest and motion.
Ans:
REST
It can be defined as:
“A body is said to be in rest if it
does not change its position with
respect to its surroundings”
MOTION
It can be defined as:
“A body is said to be in rest if it
changes its position with respect
to its surroundings”
Roka hoa matlab in rest
Motion matlab harkat mai
Q: define motion and its types.
Ans:
MOTION
It can be defined as:
“A body is said to be in rest if it changes
its position with respect to its
surroundings”
TYPES OF MOTION
There are 3 most common types of motion
1. Translator motion
2. Rotatory motion
3. Vibratory motion
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TRANSLATORY MOTION:
When a body moves in some particular paths such as linear,
circular or random. The body is said to be in rotatory motion.
e.g.
1.
a car moving on a straight
road
2.
an electron revolving
around the nucleus
3.
the Brownian motion
there are further 3 types of translatory
motion
1.linear motion
2.circular motion
3.random motion
ROTATORY MOTION:
When a body spins about its own axis
then the body is said to be in rotatory
motion.
e.g.
1.
rotation of earth
2.
motion of fan
VIBRATORY/ OSCILLATORY MOTION:
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When a body repeats its mean position in
equal interval of time then it is said to be in
vibratory or oscillatory motion.
OR
When a body possess TO and FRO motion
then it is said to be in vibratory or oscillatory motion.
e.g.
1. motion of pendulum
2. motion of a swing
Q: define translator motion and its types.
Ans:
TRANSLATORY MOTION
When a body moves in some particular paths such as linear,
circular or random. The body is said to be in rotatory motion.
e.g.
1. a car moving on a straight road
2. an electron revolving around the nucleus
3. the Brownian motions.
TYPES OF TRANSLATORY MOTION
There are 3 types of translatory motion
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1.linear motion
2.circular motion
3.random motion
LINEAR MOTION:
When a body moves in a straight path then it is
said to be in linear motion
e.g.
a car moving in a straight line
CIRCULAR MOTION:
When a body moves in a circular path then it is said to be in
circular motion
e.g.
earth revolving around the sun
RANDOM MOTION:
When a body moves in a zig zag path then it is said to be in
random motion.
e.g.
the Brownian motions.
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Q:Define kinematics.
Ans:
KINEMATICS
The word kinematics derived from Greek word 'kinema' meaning
motion. The branch of physics which deals with the motion of
objects without any reference to the force or agent causing the
motion is called kinematics.
Q: define mechanics.
Ans:
MECHANICS
Mechanics is the branch of physics that deals with the kinematics
and dynamics of objects.
Q: define dynamics.
Ans:
DYNAMICS
The word dynamics is taken from a Greek word 'dynamic'
meaning power. So dynamics is the branch of physics which deals
with the causes of motion or the factor which affect the motion.
Q.4: Define scalar and vector quantities with examples?
Ans:
SCALAR QUANTITIES
The quantities that are fully described by a magnitude (or
numerical value) alone are called scalar quantities.
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e.g.
•
•
•
•
•
•
time
speed
distance
work energy
temperature
charge
etc
VECTER QUANTITIES
The quantities that are fully described by both a magnitude and a
direction are known as vector quantities
e.g.
•
•
•
•
•
•
•
acceleration
velocity
displacement
force
weight
torque
momentum
etc
Q: define speed.
Ans
Speed
The rate of change of distance is called speed.
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Or
the rate at which someone or something
moves or operates or is able to move or
operate is called speed.
FOMULA
TYPES OF SPEED
the three types of speed are as follow
1. UNIFORM SPEED
2. VARIABLE SPEED
3. AVERAGE SPEED
UNIFORM SPEED
If a body covers equal distance in equal intervals of time then it is
said to be moving at uniform speed.
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VARIABLE SPEED
Variable speed is the distance covered by a body with
a speed which changes for a given time interval.
AVERAGE SPEED
the average of the speed of a moving object for the overall
distance is called average speed.
Q: define velocity.
Ans
VELOCITY
The rate of change of displacement is called velocity.
Or
the VELOCITY of something in a given direction.
FORMULA
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VELOCITY
TYPES OF VELOCITY
the three types of VELOCITY are as follow
1. UNIFORM VELOCITY
2. VARIABLE VELOCITY
3. AVERAGE VELOCITY
UNIFORM VELOCITY
If a body covers equal distance in equal intervals of time then it is
said to be moving at uniform VELOCITY.
VARIABLE VELOCITY
Variable VELOCITY is the distance covered by a body with
a VELOCITY which changes for a given time interval.
AVERAGE VELOCITY
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the average of the VELOCITY of a moving object for the overall
distance is called average VELOCITY.
Q: define acceleration.
ANS:
ACCELERATION
The rate of change of velocity is called
acceleration
• It is a vector quantity
• It can be calculated as a=v/t
• Its SI unit is m/s2
TYPES OF ACCELERATION
There are following types of acceleration
POSITIVE ACCELERATION
Positive acceleration is the change in velocity of an object in
the positive direction, as defined for the system.
NEGATIVE ACCELERATION
Negative acceleration is the change in velocity of an object in
the negative direction, as defined for the system.
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UNIFORM ACCELERATION
If an object's speed (velocity) is increasing at a constant rate
then we say it has uniform acceleration.
Q: define deceleration or retardation.
Ans:
DECELERATION/RETARDATION
The negative of acceleration is called
deceleration or retardation.
• It is a vector quantity
• It can be calculated as -a=v/t
• Its SI unit is m/s2
Q:define motion under gravity.
Ans:
MOTION UNDER GRAVITY
when an object appears to be falling under
the influence of gravity then the motion is
said to be the motion under gravity.
• Where distance (s) changes into height
(h) and acceleration (a) changes into
gravitational acceleration (g).
Q: define gravitational acceleration and sign convension
of gravitational acceleration (g).
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Ans:
Gravitational Acceleration
the acceleration due to gravity is known as
gravitational acceleration.
• It is represented by g
• Its SI unit is m/s2
• Its value is 9.8 m/s2 (g=9.8 m/s2)
SIGN CONVENSION OF g
• The value of g is taken as positive when the object moves
upwards to downwords
• The value of g is taken as negative when the object moves
downwords to upwards
• The value is 9.8 m/s2 (g=9.8 m/s2)
• Its SI unit is m/s2
SNO
1
2
3
4
DIFFERENCES
SPEED
VELOCITY
The rate of change of
distance is called speed
It is a scalar
quantity
It can never be negative
or zero
It is the distance
covered per unit time
The rate of change of
displacement is called velocity
It is a vector quantity
It can be negative or zero
It is the displacement covered
per unit time
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SNO
1
2
3
4
DISTANCE DISPLACEMENT
the length of a path
between any 2 points is
called distance
It is a scaler quantity
The shortest distance is called
displacement
It can never be negative
or zero
It is denoted by s
It can be negative or zero
It is a vector quantity
It is denoted by v
Q: derive equations of motion.
Ans:
EQUATION OF MOTION:
Relation among velocity, distance, time and acceleration is called
equations of motion. There are three equations of motion:
First Equation of Motion:
The final velocity (vf) of a moving object with uniform
acceleration (a) after time, t.
Let, the initial velocity = Vi.
Final velocity = Vf.
Time = t
Acceleration = a
We know that, Acceleration (a) =Change in velocityTime
taken=Change in velocityTime taken
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⇒a=Final velocity-Initial velocityTime taken
⇒a=Final velocity-Initial velocityTime taken
⇒a=Vf−Vit
⇒a=Vf-Vit
⇒at=Vf−Vi
⇒at=Vf-Vi
⇒at−Vf=−Vi
⇒at-Vf=-Vi
⇒−Vf=−Vi−at
⇒-Vf=-Vi-at
⇒Vf=Vi+at
⇒Vf=Vi+at ---(i)
This equation is known as first equation of
motion.
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Second Equation of Motion
Distance covered in time (t) by a moving body.
Let, Initial velocity of the object = Vi
Final velocity of the object = Vf
Acceleration = a
Time = t
Distance covered in given time = s
We know that,
Average velocity =Initial velocity+Final velocity
2
=Initial velocity+Final velocity
2
∴ Average velocity =Vi+Vf =Vi+Vf----(ii)
2
2
We know that, Distance covered (s) in given time = Average
velocity x Time
Or, s = Average velocity x Time -----------------(iii)
After substituting the value of average velocity from equation (ii)
we get
⇒s=Vi+Vf×t
2
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⇒s=Vi+Vf×t
2
After substituting the value of ‘Vf’ from first equation of motion
we get,
⇒s=Vi+(Vi+at)×t
2
⇒s=Vi+(Vi+at)×t
2
⇒s=Vi+Vi+at×t
2
⇒s=Vi+Vi+at×t
2
⇒s=2Vi+at×t
2
⇒s=2Vi+at×t
2
⇒s=2Vit+at2
2
⇒s=2Vit+at2
2
⇒s=2Vit +at2
2
2
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⇒s=Vit+1at2
2
The above equation is known as Second equation
of motion.
Third Equation of Motion
The third equation of motion is derived by substituting the value
of time (t) from first equation of motion.
We know the formula of distance s=Vav x t
As we know
Vav=Vi+Vf
2
Therefore; s=( Vi+Vf ) x t
2
Since; t=Vf-Vi
a
Therefore by substituting the values we get
S=( Vi+Vf ) x ( Vf-Vi )
2
a
S=( Vf+Vi ) x ( Vf-Vi )
2a
since;(a+b)(a-b)=a2+b2
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S=Vf2 – Vi2
2a
2aS= Vf2 – Vi2
This is called the Third equation of motion
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CHAPTER NO. 4
PHYSICS NOTES
CLASS MATRIC
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Q: define force.
Ans:
FORCE
Force is an agent which changes or tends to
change the state
of rest or of uniform motion of a body.
OR
Force acting on a body is equal to the product of the
mass and acceleration produced in the body.
• Force can accelerate or decelerate a
body.
• Force is a vector quantity.
FORMULA
F = ma
UNITS OF FORCE
(i) NEWTON (N) in S.I system
(ii) DYNE in C.G.S system
(iii) POUND (Lb) in BRITISH ENGINEERING SYSTEM (F.P.S)
Q: define newton.
NEWTON
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Newton is the unit of force and can be defined as:
"The amount of force that produces an acceleration of
1 m/s2 in a body of mass 1-kg is equal to 1 NEWTON."
1 N = 1 kg x 1m/s2
[ N = kg m/s2]
Q: state newton’s first law of motion.
Ans:
Newton’s First Law Of Motion
“Every body continues its state of
rest or of uniform motion unless it
is acted upon by some external
force which changes its state of
rest or of uniform motion”
EXAMPLE:
First law of motion consists of two parts:
PART NO 1
The first part states that a body at rest
remains at rest unless an external force act
upon it.
This part is in accordance with our
common experience for example, a book
lying on a table remains at rest unless it is
lifted or pushed by an external force.
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PART NO 2
Second part states that a body in motion
remains in motion with uniform velocity
unless an external force act upon it.
This part is not self-evident because a ball
pushed once does not continue its motion
forever. A little consideration however,
shows that there is an opposing force like
ground friction and air friction acting in this case. These frictional
forces are responsible to stop the ball. If we eliminate these
opposing forces, a body in motion will continue its motion forever.
Q: state and explain Newton’s second law of motion.
Ans:
NEWTON’S SECOND LAW OF MOTION.
It can be stated as
“When a force acts on an object it produces
an acceleration, which is directly proportion
to the amount of the force and inversely
proportional to the product of mass”
MATHEMATICALLY
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Combining (i) and (ii)
....
a = k (F)(1)
m
here
constant k=1
a= (1)(F)(1)
m
a=F
m
ma= F
we get,
EXPLANATION
The net force acting on a body is equal to the product of the
mass of body and the acceleration produced in it.
EXAMPLE
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A motorcycle is accelerating due to the
force in the engine the greater the force
in the engine the greater the
acceleration is produced whereas the
greater the mass is loaded on the bike /
motor cycle the lesser the acceleration is produced.
Q: state and explain Newton’s third law of motion.
Ans:
NEWTON’S THIRD LAW OF MOTION
It can be stated as
“To every action there is an equal and
opposite reaction”
This Photo by
EXAMPLES
1. Motion of rocket: fuel burns rapidly, exerts force
in downward direction and rocket moves upward
as a reaction.
2. Book lying on a table: weight of the book on
the surface is action and the force exerted
by the surface (R) is the reaction.
R = -W
3.Walking on a street
4.Motion of helicopter
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Q: define inertia.
Ans:
INERTIA
Inertia is the tendency of a body to resist a change in
its state.
EXAMPLE
• If a driver suddenly applies the brakes in a fastmoving car the passengers will move forward due
to inertia
• If a boy will jump from a fast-moving bus he will
also run in the direction of bus after the jump due
to inertia
Q: define mass.
Ans:
MASS
The quantity of matter in a body is called its mass.
• Mass is a scalar quantity.
• Mass of a moving body is m=F/a.
• Unit of mass in S.I system is KILOGRAM (kg)
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Q: define weight.
Ans:
WEIGHT
Weight is the force by which the earth attracts a body towards
its center.
• Weight is a vector quantity
• Weight of a body vary place to place and
become zero on the center of earth and far away
from the surface of earth
• Weight of a body is W = mg.
• Unit of weight in S.I system is NEWTON (N).
Q: define tension.
Ans:
TENSION
The force experienced by a string or a rope when it
is stretched is called tension
• It is denoted by (T)
• Its SI unit is newton (N)
Q: derive an expression for (tension) in a string and
acceleration produced in bodies when:
BOTH BODIES HANG VERTICALLY
Consideration:
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Consider two bodies of unequal masses m1 and
m2 connected by the ends of a string, which
passes over a frictionless pulley as shown in
the diagram.
If m1>m2, the body ‘A’ will move downward with
acceleration ‘a’ and the body ‘B’ will move up
with same acceleration. Here we have to find
the value of ‘a’ and tension ‘T’.
FORCES ACTING ON BODY A
There are two forces acting on A
(i)Weight of body: w1 = m1g
(ii) Tension in the string = T
The net force acting on the body is
F= m1g – T
Net force acting on body 'A' is given by Newton’s 2nd law as m1a.
Thus we have the equation for the motion of body "A" as:
m1g – T = m1a --------- (i)
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FORCES ACTING ON BODY B
There are also two forces acting on B
(i)Weight of body: w2 = m2g
(ii) Tension in the string = T
Since body "B" is moving up, the net force acting on body is
F= T – m2g
T – m2g = m2a---------- (ii)
Adding (i) & (ii)
(m1 – m2)g = (m1 + m2)a
putting the value of 'a' in equation (ii) to find the magnitude of T
T – m2g = m2a
T – m2g = m2
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Case 2
ONE BODY MOVES VERTICALLY AND OTHER MOVES
HORIZONTALLY
Two bodies A & B of masses m1 and m2 are attached to the ends
of a string, which passes over a frictionless pulley as shown in
the figure. The body "A" moves vertically downward with
an acceleration equal to "a" and the body "B" moves on a
smooth horizontal plane towards the pulley with the same
acceleration.
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Consider the motion of body A
Forces acting on the body A
1. Weight of the body: w1 = m1g
2. Tension in the string = T
The net force acting on the body A
m1g – T
the resultant force acting on it is equal to m1a
Therefore,
m1g – T = m1a --------- (i)
Now Consider the motion of body B
There are three forces acting on it.
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1. The tension (T) in the string, which acts horizontally
towards the pulley.
2. Its weight w2 = m2g which acts vertically downward
3. Reaction of the surface (R) on the body which acts
vertically upward.
As there is no motion of body "B" in the vertical direction.
Therefore, weight and normal reaction cancel each other
For latest information,
Thus, the net horizontal force acting upon body B is T
T = m2a --------(ii)
Putting the value of T in equation (i), we get
m1g – m2a = m1a
m1g = m1a + m2a
m1g = a (m1 + m2)
Putting the value of "a" in equation (ii), we get
T = m2a --------(ii)
T = m2
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Q: define momentum and describe law of conservation of
momentum.
Ans:
MOMENTUM
The quantity or quality of motion is called
momentum and it is denoted by P
OR
It is the product of mass and velocity.
MATHEMATICALLY
P = mV
where:
p is the momentum
m is the mass
v the velocity
LAW OF CONSERVATION OF MOMENTUM
STATEMENT
it states that
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“The total momentum of an isolated
system always remains constant.”
DERIVATION
Consideration
Consider two bodies A and B of mass m1 and
m2 moving in the same direction with velocity
U1 and U2 respectively such that U1 is greater
than U2. Suppose the ball acquire velocity V1
and V2 respectively
after collision
Momentum of the system before collision = m1U1 + m2U2
Momentum of the system after collision = m1V1 + m2V2
According to the law of conservation of
momentum:
Total momentum of the system before collision = Total
momentum of the system after collision
=>m1U1 + m2U2 = m1V1 + m2V2
Q: define friction.
Ans:
FRICTION
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When a body moves over the surface
of another body then the opposing
force is produced and this opposing
force is called force of friction
Or
The force which opposes the motion of a
body while in contract with the other body
is known as friction.
Example
Suppose a wooden block is placed on a table and a
spring balance is attached on it. If we apply a very
small force of magnitude F by pulling the spring
gradually and increase it, we observe that the block
does not move until the applied force has reached a
critical value. If F is less then critical value, the
block does not move. According to Newton’s Third
Law of motion an opposite force balance the force.
This opposing force is known as the force of friction
or friction.
Q: define static friction.
Ans:
STATIC FRICTION
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the resisting force between two surfaces before the motion start
is called static friction
Q: define limiting friction.
Ans:
Limiting Friction
the maximum value of static friction
within which the motion of the body is
about to start is called limiting friction.
Or
When an external force is applied against the force of friction, the
force of friction also increases by the same amount. Therefore, it
adjusts itself in such a way that it is equal and opposite to the
external force. It has a maximum value just before the motion
starts. So, friction is a self-adjusting force. The maximum force of
friction that stops the body from moving is called LIMITING
FRICTION.
It is denoted by Fs.
LIMITING FRICTION is directly proportional to the surface
reaction.
Limiting friction Fs is:
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Where R = normal
reaction
but R = W
and R = mg
Where
= constant known as coefficient of friction.
Q define rolling friction.
Ans:
Rolling friction
When a body rolls over a surface, the
force of friction is called ROLLING
FRICTION. When a sphere rolls over a
surface it experiences an opposing force
called ROLLING FRICTION.
Rolling friction is much less than the This Photo by Unknown Author is
licensed under CC BY-NC-ND
sliding friction because in case of rolling
contact area of two surfaces is very small as compared to sliding.
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Q: define kinetic friction.
Ans:
KINETIC FRICTION
The force of friction which is produced during the motion is called
kinetic friction it is slightly less than the limiting friction.
Q: define coefficient of friction.
Ans:
Coefficient Of Friction
Coefficient of friction is the ratio of LIMITING FRICTION to the
NORMAL REACTION.
Coefficient of friction is constant for a given pair of surfaces but
different for different pairs
Unit of
:
Since it is a ratio of two similar quantities, therefore it has no
unit.
Q: define Causes of Friction.
Causes of Friction
If we see the surface of material bodies through microscope, we
observe that they are not smooth. Even the most polished
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surfaces are uneven. When one surface is placed over another,
the elevations of one get interlocked with the depression of the
other. Thus they oppose relative motion. The opposition is known
as friction.
Q: define Factors on which Friction Depends.
Factors on which Friction Depends
The force of friction depends upon the following factors:
1. Normal Reaction (R)
Force of friction is directly proportional to normal reaction (R),
which act upon the body in upward direction against the weight
of the body sliding on the surface.
2. Nature of Surfaces
Force of friction also depends
upon the nature of the two
surfaces. It is denoted as u and
has constant values for every
surface. It is different for the two
surfaces in contact.
Q describe advantages and disadvantages of friction.
ADVANTAGES OF FRICTION
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• We could not walk without the friction
between our shoes and the ground. As
we try to step forward, we push your
foot backward. Friction holds our shoe to
the ground, allowing you to walk.
• Writing with a pencil requires friction. we
could not hold a pencil in our hand without
friction.
• A nail stays in wood due to friction
• Nut and bold call hold due to friction
DISADVANTAGES OF FRICTION
• In any type of vehicle–such as a car,
boat or airplane–excess friction means
that extra fuel must be used to power
the vehicle. In other words, fuel or
energy is being wasted because of the
friction.
• Due to the friction a machine has less
frequency 100%
• Due to friction machine catch fire.
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• Due to friction wear and tear occurs in shoes and
tires etc
Q: describe methods to remove friction.
Ans:
Methods to remove friction
Friction can be removed or reduced by the following methods:
1. The various parts of the machines that are moving over one
another are properly lubricated.
2. In machines, the sliding of various parts is usually replaced by
rolling. This is done by using ball bearings.
3. Where sliding is unavoidable, a thick layer of greasing material
is used between the sliding surfaces.
4. The front of the fast-moving objects, e.g. cars, aero planes are
made oblong to decrease air friction.
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