Matric Part 1/9th Class Physics Chapter 3 Long Question With Answer for Unit 3 Dynamics

Question # 1

Explain Centripetal force and Drive F_c= mv²/r.

Ans 1: A force that keeps a bodyto move in a circle is known as centripetal force.
Explanation:
Consider a body tied at the end of a string moving with uniform speed in a circular path. A body has the tendency to move in a straight line due to inertia. The string to which body is tied keeps it to move in a circle by pulling the body towards the center of the circle. The sting pulls the center of the circle .the string pulls the body perpendicular to its motion. The pulling force continuously changesthe direction of motion and remains towards the center seeking force is called the centripetal force.
Equation:
Fc = ma,
So ma,+ mv²/r
a,=v²/r

Question # 2

Define dynamics, also briefly explain force , inertia and momentum

Ans 1: Dynamics: the branch of mechanics that deals with the study of motion fo an object and cause of its motion is called dynamics
Ans 2: Force: A force moves or tends to move, stops or tends to stop the motion of a body. The force can also change the direction of motion of a body. IT is represented by F. Its S>I unit is Newton, it is a vector quantity
Example: A door can be opened or closed by pushing or pulling it
Goal keeper need a force to stop a ball coming to him
A batsman change the direction of moving ball buy pushing it with bat
Note: A force can also change the the shape or size of a body on which it acts
Ans 3: Inertia: inertia of a body is its property due to which it resists any change in its state of rest or motion
Explanation: Galileo observed that it is easy to move or to stop light objects than heavier ones. newton concluded that everybody resist to change in its state of rest or uniform motion in straight line. This property of matter is inertia.
Example: Take a glass cover it with a piece of cardboard, place a coin on the cardboard. Now flick the card horizontally with a jerk of your finger. Card board will fly away but coin will not move with card board de to inertia and will fall into glass
Cut a strip of paper , place it on a table, stack a few coins at its one end . pull out the paper strip under coins with a jerk, coin remain stacked on pulling out the strip quickly due to inertia
Ans 4: Momentum: Momentum of a body is the quantity of motion it possesses due to its mass and velocity
OR
The product of mass and velocity is known as momentum
Mathematical form: its formula is P=mv
Momentum is a vector quantity. Its direction will be sae in which body moves. Its S.I unit is Ns

Question # 3

Derive tension and acceleration when one body move vertically and other body move horizontally

Ans 1: Consider two bodies A and B of masses m1 and m2 respectively attached to the ends of an inextensible string. Let the body A moves downward with an acceleration a. Since string is inextensible , therefore, body B also moves over the horizontal surface with the the same acceleration. As the pulley is frictionless, hence tension T will be the same throughout the string.
Ans 2: Body A : since body A moves downward, therefore, its weight m11g is greater than the tension T in the string. Net force acting on body A =m1g-TF=m1aby comparing both we getm1g-T= m1a
Ans 3: Body B: the force acting on body B are:weight m2g of the body B acting downward.Reaction R of the horizontal surface acting on body B in the upward directionTension T in the string pulling the body B horizontally over the smooth surfaceas body B has no vertical motion, hence resultant of vertical forces(m2g and R) must be zero.Thus, the net force acting on body B is TAccording to Newtons second law of motionT=m2aby addingm1g-T+T= m1a+m2am1g=m1a+m2am1g=a(m1+m2)a+m1g/m1+m2by putting the value of a in equation to get tension TT= m2(m1g/m1+m2)T=m1m2g/m1+m2

Question # 4

define and explain friction

Ans 1: Friction: the force that opposes the motion of moving objects is called frictionFactors: in case of solid, forces of friction between two surfaces depends upon many factors such as:nature of two surfaces in contactpressing force between them
Ans 2: Explanation: No surface is perfectly smoot. A surface that appear smooth has pits and bumps that can be seen under a microscope, the contact points between two surfaces form a sort of cold welds there cold welds resist the surfaces from sliding over each other. Adding weight over the surface increase the pressing force that increase the resistance.Limiting friction: maximum value of friction is known as force of limiting friction
Ans 3: Mathematical form: Let a body is at rest if a force is applied to body and body remains at rest then the friction is equal to the applied force that tends tot move a body at rest, it increases with t applied force. Friction can be increased to certain maximum value it does not increase beyond this. This maximum value of friction is force of limiting friction. It depends on normal reaction( pressing force ) between two surface in contact
Ans 4: Coefficient of friction: ratio between the force of limiting friction Fs and normal reaction R is constant. This constant is called the coefficient of friction. Coefficient of frication has no unit as it is a ration between two same quantitates.
Ans 5: Uses of friction: friction is needed to walk on the ground. it is risky to run on wet floor with shoes that have smooth soles. Athletes use special shoes that have extraordinary ground grip. Such shoes prevent them from slipping while running fast .To stop a bicycle we apply breaks the rubber pads pressed against the rims provide friction. it is the friction that stops the bicycle.

Question # 5

How you can relate a force with the change in momentum of a body

Ans 1: Consider a body of mass m moving with initial velocity vi. Let a force F acts on the body which produces an acceleration a in it. The changes the velocity of the body. Lets its final velocity after time t become vf. Ig pi and pf be the initial momentum and final momentum of the body related to initial and final velocities arepi=mvipf=mvfchange in momentum= final momentum- initial momentumpf-pi= mvf-mvi

Question # 6

Explain law of conservation of momentum

Ans 1: Statement: The momentum of an isolated system of two or more than two interacting bodies remains constant
Ans 2: Isolated system: An isolated system is a group of interacting bodies on with no external force is acting
Ans 3: Explanation: Consider an isolated system of two spheres of masses m1 and m2. They are moving in a straight line with initial velocities u1 and u2 respectively such that u1 is greater than u2 sphere of mass m1 approaches the sphere m2 as they moveinitial momentum of mass m1= m1u1initial momentum of mass m2= m2u2Total initial momentum of the system before collision =m1u1+m2u2After sometime mass m1 hits m2 with some force. According to Newton's third law of motion, m2 exerts an equal and opposite reaction force on m1. Let their velocities become v1 and v2 respectively after collision. Thenfinal momentum of mass m1=m1v1final momentum of mass m2= m2v2Total final momentum of the system after collision=m1v1+m2v2................by comparing we get Total initial momentum of the system before collision= total momentum of the system after collisionm1u1+m2u2=m1v1+m2v2..............AEquation A shows that the momentum of an isolated system before and after collision remains same which is the law of conservation of momentum. Law of conservation of momentum is an important law and has vast applications

Question # 7

Explain braking and skidding

Ans 1: The wheels of moving vehicles have two velocity componentsmotion of wheels along the roadrotation of wheels about their axisto move a vehicle on the road as well as to stop a moving vehicle requires friction between its tyres and the road. For example, if the road is slippery or the tyre are worn out then the typre instead of rolling, slip over the road,The vehicle will not move if the wheels starts slipping at the same point on the slipper ty road. Thus for the wheels to roll, the force of friction9gripping force 0 between the tyres and the road must be enough that prevents them from slipping.if we want to stop a car quickly, a large force of friction between the tyres and the road is needed. But there is a limit to this force of friction that tyres can provide. If the breaks are applied too strongly, The wheels of th car will lock up ( stop turning) and the car will skid due to its large momentum. If we want t o reduce the skidding, it is necessary not to apply breaks too hard that lock up their rolling motion. It is unsafe to derive a vehicles wit worn out tyres .

Question # 8

Explain Newtons second law of motion

Ans 1: When a net force acts on a body, its produces acceleration in the body in the direction of the force. The magnitude of this acceleration is directly proportional to the net force acting on the body and inversely proportional to its mass
Ans 2: Newton: One newton is the force that produces an acceleration of 1 ms-2 in a body of mass 1 kg1N= 1kg * 1ms-2or 1 N = 1kgms-2

Question # 9

how much centripetal force is needed to make a body of mass 0.5 kg to move to a circle of radius 50cm with a speed 3 ms-¹

Ans 1:
m= 0.5kg
r = 50cm = 0.5m
v = 3ms-¹
Fc=?
As we know that
Fc= mv²/r
Fc = 0.5 x(3)²/0.5
Fc = 4N

Question # 10

Explain law of conservation of momentum? Also drive its formula?

Ans 1: The momentum of an isolated system of two or more than two or more than two interacting bodies remain constant.
An isolated system is a group of interacting bodies on which no external force is acting . IF no unbalanced on net force acts on a system then its momentum remains constant.
Consider a system of gun and a bullet. Before firing, the Velocity of the bullets as well as that of gunwas zero. therefore the total momentum of both the objects was also zero.
we can write it as,
Total momentum of gun and bullet before fixing =0
When the gun is fired bullet shoots out of guns and acquire momentum.To converse momentum the qunrecoils backward. Now according to the law of conversation of momentum, the total momentum of the gun and bullet will also be zero after the gun is fired.
let m be the mass of the bullet and v be its velocity on firing the gun; M be the mass of the gun and V is the Velocity with which it recoids. thus the total momentum of the gun is fired will be: The momentum of the gun and the bullet after the gun is fired = Mv+ mv
According to the law of conversation of momentum.
Total momentum before firing = Total momentum after firing
MV + mv=0
Mv =-mv
or v=-m/M v

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Matric Part 1/9th Class Physics Chapter 3 Long Question With Answer for Unit 3 Dynamics

9th Class English Medium Subjects

9th Class Urdu Medium Subjects

Online Long Questions For Chapter 3 "9th Class Physics Chapter 3 Long Question Preparation "

Physics (New Book) - 9th Class Physics Chapter 3 Long Question Preparation

Explain Centripetal force and Drive Fc= mv2/r.

Define dynamics, also briefly explain force , inertia and momentum

Derive tension and acceleration when one body move vertically and other body move horizontally

define and explain friction

How you can relate a force with the change in momentum of a body

Explain law of conservation of momentum

Explain braking and skidding

Explain Newtons second law of motion

how much centripetal force is needed to make a body of mass 0.5 kg to move to a circle of radius 50cm with a speed 3 ms-¹

Explain law of conservation of momentum? Also drive its formula?

Prepare Complete Set Wise Questions For Chapter 3 "9th Class Physics Chapter 3 Long Question Preparation "

Set 1

Set 2

9th Class Physics Chapter 3 Long Question Preparation - Set 1

Explain Centripetal force and Drive Fc= mv2/r.

Define dynamics, also briefly explain force , inertia and momentum

Derive tension and acceleration when one body move vertically and other body move horizontally

define and explain friction

How you can relate a force with the change in momentum of a body

Explain law of conservation of momentum

Explain braking and skidding

Explain Newtons second law of motion

how much centripetal force is needed to make a body of mass 0.5 kg to move to a circle of radius 50cm with a speed 3 ms-¹

Explain law of conservation of momentum? Also drive its formula?

9th Class Physics Chapter 3 Long Question Preparation - Set 2

Write third law of motoin. explain it with examples

Write note on application of centripetal force

Define dynamics, also briefly explain force , inertia and momentum

How you can relate a force with the change in momentum of a body

Explain Centripetal force and Drive Fc= mv2/r.

Write differences between mass and weight

Explain gun and bullet system using law of conservation of momentum

Explain law of conservation of momentum? Also drive its formula?

Define and explain centripetal force

Write the advantages and disadvantages of friction, also give methods to reduce friction

9th class Physics Chapter 3 Long Q's (English Medium)

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Explain Centripetal force and Drive F_c= mv²/r.

Explain Centripetal force and Drive F_c= mv²/r.

Explain Centripetal force and Drive F_c= mv²/r.