Ch#3 PHYSICS CLASS 9 Dynamics
BY MUHAMMAD RASHEED (THE EDUCATOR RACHNA CAMPUS)
FAREED FIDA (IQ LEARNING SCHOOLS)
MCQ’S
(i)Newton first
law of motion is valid only in absence of
a. Force b. Net force c. Friction d.
Momentum
(ii)Inertia
depends upon
a.Force b.Net force c. Mass d.
Velocity
(iii)A boy
jumps out of a moving bus there is a danger for him to fall
a. Towards a
moving bus b. away from
bus c. indirection
of motion d. opposite to the direction of motion
(iv)A string is
stretched by two equal and opposite forces of 10 N each the tension in the
string is
a.Zero b. 5 N c. 10 N d.
20 N
(v)Mass of a
body
a.Decreases
when accelerated b. increases
when accelerated c. Decreases
when moving with high-velocity d.
none
(vi)Two bodies
of masses, m1and m2 attached to the ends of an inextensible string passing over
a frictionless pulley such that both move vertically a is
a. b. c. d.
(vii)Which of
the following is the unit of momentum
a? Nm b. Kgm/s2 c. Ns d.
N/s
(viii)When the horse pulls a cart the action is own
a. Cart b. Earth c. Horsed.
Earth & Cart
(ix)Which of
the following material lower friction when pushed between metal plates?
a.Water b. Fine marble powder c. Air d. Oil
Short Questions & Numerical Q # 3.2 Define the following terms
(i) Inertia (ii) Momentum (iii) Force
(iv) Force of friction (v) Centripetal
force
Answer (i)Inertia
a body shows resistance in its state of change, this
property is called inertia
(ii) Momentum
It is given
as P = mv
Its unit is km/s
also called Ns.
(iii)Force
A force moves or tends to move stops or tends to stop the motion of the body.
(iv) Force of
friction
The opposing force between the surfaces of two moving
objects are called the force of friction.
(v) Centripetal force
Q # 3.3 What is the difference between?
(i) Mass and
weight (ii) Action and reaction
(iii) Sliding
friction and rolling friction
Answer (i)Mass and weight
Mass of a body is the amount of be counted possessed via the
body. It is a scalar quantity and does
now not alternate with the exchange of location.
It is measured with the aid of contrast with popular loads the use of a
beam balance.
Weight of a frame is the pressure of gravity appearing on
it. On the Earth, the weight of a body is
identical to the force with which Earth attracts it. It varies depending upon the cost of g,
acceleration because of gravity. Weight
is pressure and consequently, it's miles a vector quantity.
(ii) Action and response
(iii) Sliding
friction and rolling friction
Sliding friction
The opposing pressure of moving objects when the object is
sliding over a floor then friction is called sliding friction
Rolling friction
When an item is rolling over a surface then its friction is
referred to as rolling friction, like the friction of a wheel at the floor of the avenue. Rolling friction is a whole lot
smaller than sliding friction.
Q # three.Four What is the regulation of Inertia?
Answer Law of Inertia
Everybody resists to the alternate in its country of rest or
of uniform motion in an immediate line, extra the mass of a frame extra might
be the inertia of a frame it's far called the law of inertia, 1st law of movement
is also called regulation of inertia.
Q # 3Why is it dangerous to tour on the roof of a bus?
Answer While
visiting on the roof of a bus, it is dangerous due to the fact when a bus takes
a flip shifting with fast speed, the passenger moves inside the route of motion
due to inertia and might circulate outwards.
Q # three. Why does a passenger flow outward whilst a bus takes a flip?
Answer While
visiting on the roof of a bus, it's far dangerous because when a bus takes a turn shifting
with rapid pace, the passenger movements within the path of movement because of
inertia and may pass outwards.
Q # three.7 How
can you relate pressure with the exchange of momentum of a body?
Answer Force
is identical to the rate of alternate in the momentum of a body.
As
trade in momentum = mVf - mVi
Rate of trade in momentum = mVf - mVi / t
= m( Vf – Vi) /t
= ma
= F
Rate of exchange in momentum is the same to force applied on
frame.
Q # three.8 What
maybe the anxiety in a rope that is pulled from its ends by contrary forces a hundred N every?
Answer Tension
within the string can be 0 below the movement of identical and contrary forces, due to the
fact same and opposite forces cancel the
impact of each different.
Q # 3.9 Action and
response are usually equal and opposite.
Then how does body actions?
Answer Action
and response is always the same and contrary however motion acts on one frame even
as a reaction on every other body, so a body can flow because of action and response.
Q # 3.10 A
horse pulls the cart. If the movement
and reaction are equal and opposite then how does a cart circulate?
Answer Push
of a horse is the motion of horse on this planet but the response of earth on the pony
and cart permits the movement of horse and cart. So a horse pulls the cart.
Q # 3.11 What
is the law of conservation of momentum?
Answer In
a remoted machine momentum of the machine is continually consistent i.E. If two
are more than gadget collide then
general momentum earlier than collision and after collision stays constant,
this is called the law of conservation of momentum.
Q # three.12Why
is the regulation of conservation of momentum crucial?
Answer According
to the regulation of conservation of momentum in a remoted system momentum earlier
then and after collision remains steady so we can effortlessly discover initial
or very last speed before or after momentum.
Q # 3.Thirteen When a
gun is fired, it recoils. Why?
Answer When
a gun is fired it recoils due to response. The motion of the bullet ahead route is
movement and recoiling of a gun in backward is a response. As movement and reaction
are constantly identical in magnitude but contrary in a direction so a gun
recoils to preserve the momentum.
Q # three.14 Describe
two conditions wherein pressure of friction is wanted.
Answer i) A force of friction is wanted to
stroll on this planet.
Ii) Force of
friction is needed to use brakes in transferring vehicles.
Q # three.15 How
does oiling the shifting components of a machine lowers friction?
Answer; By oiling the transferring elements of equipment
sliding contacts can without problems slip over one a different so, sliding
friction reduces.
Q # three.16Describe
ways to reduce friction.
Answer: Ways
to lessen friction.
- I) By making the sliding surfaces easy.
- Ii) By making streamline form of speedy transferring gadgets.
- Iii) By lubricating the sliding surfaces.
- Iv) By the use of ball bearings.
Q # three.17Why
rolling friction is less than sliding friction?
Answer In
sliding friction a big variety of factors are in touch among two surfaces at
the same time as in rolling friction just a few factors are in touch between
two surfaces and rolling does now not rupture bloodless welds so rolling friction
is smaller than sliding friction.
Q # 3.18 What
you know approximately the following.
- (i) Tension in a string
- (ii) Limiting pressure of friction
- (iii) Braking pressure
- (iv) Skidding of motors
- (v) Seatbelts
- (vi) Banking of roads
- (vii) Cream separator
Answer (i)Tension in a string
Let us consider a block supported by string and W is weight
of a block, weight is acting downward an equal force to weight is acting on the
string upward is called tension in a string.
(ii)Limiting
force of friction
The maximum value of friction is called limiting friction it
is denoted by Fs .limiting friction does not allow a body to move. A body can
only move if the externally applied force is greater than sliding friction.
(iii) Braking
force
To stop a Car or Bus quickly a large force of friction is
required called braking force. Breaking force is much important while driving a
vehicle.
(iv) Skidding
of vehicles
While applying strong brakes on a slippery surface vehicle’s
wheels start slipping over the surface. This
is called skidding of vehicles. While skidding a vehicle loses its directional
control so it is always dangerous to drive over a wet road or to apply strong
breaks.
(v) Seatbelts
They are safety belts. They absorb the momentum of passengers
in case of an accident and provide safety to the passengers.
(vi) Banking of
roads
Banking of roads means to raise the outer edges of roads in
curved paths to provide the necessary centripetal force to vehicles. When a car
or bus takes a turn across a curved road while moving with fast speed then it
is always risky because necessary centripetal force becomes insufficient in
such a case, so road on curved paths is banked.
(vii) Cream
separator
A cream separator is high-speed spinner acts on the principle
of centrifuge machine used to separate cream from milk.
Q # 3.19 What
would happen if all friction suddenly disappears?
Answer It
will not be possible to work, to walk even to write if all the friction
suddenly disappears.
Q # 3.20 Why
the spinner of a washing machine is made to spin at very high speed?
Answer The
spinner of a washing machine is made to spin at very high speed to provide
maximum centripetal force to cloths.
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