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

Question # 1

Write third law of motoin. explain it with examples

Ans 1: Statement: to every action there is always an equal but opposite reaction
Ans 2: Explanation: Newtons third law f motion deals with the reaction of a body when a forces acts on it. Let a body A exerts a force on another body B, the body B reacts against this force and exerts a force on body A. The force exerted by body A on V is the action force whereas the force exerted by body B on A is called the reaction force.
Ans 3: Example: Consider a book lying on a table. The weight of the book is acting on the table in the downward direction. This is the action. The reaction o f the table acts on the book in the upward direction. Take an air filled balloon. when the balloon is set free, the air inside it rushes out and the balloon moves forward. In this example, the action is by the balloon that pushes the air out of it when set free. The reaction of the air which escapes out from the balloon acts on the balloon. it is of the air which escapes out from the balloon acts on the balloon. It is due to this reaction of the scaping air that moves the balloon forward.

Question # 2

Two masses 26 Kg and 24 kgare attachedto the ends ofstringwhich passes over a frictionless pulley. 26 kg islayingover a smooth horizontal table. 24 N mass is

Ans 1: Solution
₁= 24kg
₂=26 kg
= 10ms-²
Solution;
a= m₁g/m₁ +m₂
a= 24x10/24+26
a =240/50
a =4.8ms-²
T =m₁ m₂ g/m₁ +m₂
T= 24x26x10/24+26
T= 6240/50
T = 124.8N
T =125 N

Result:
a=4.8ms-²
T= 125N

Question # 3

Explain gun and bullet system using law of conservation of momentum

Ans 1: consider a gun and bullet system before firing the gun, both gun and bullet are at rest so the total momentum of system is zero.As the gun is fired bullet shoots out of the gun and acquires momentum. To conserve momentum of system the gun recoils. According to law of conservation of momentum, the total momentum of gun and bullet will also be zero after gun is fired . Let m be the mas of bullet and v be its velocity on firing the gun. M be the mass of gun and V be the velocity of gun with which it recoils'Total momentum of the gun and the bullet after the gun is fired = MV+mvaccording to law of conservation of momentumTotal momentum of gun and bullet after fire= Total momentum of gun and bullet before fireMV+mv=0MV=-mv
Ans 2: Note: negative sign indicates that velocity of gun is opposite to velocity of bullet, gun recoils. since mass of gun is much larger than the bullet therefore, the reoil is much smaller than the velocity of bullet

Question # 4

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 # 5

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 # 6

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 # 7

Derive relation for tension and acceleration when two bodies moving along vertically

Ans 1: Consider two bodies A and B of masses m1 and m2 respectively. Let m1 is greater than m2. The bodies are attached to the opposite ends of an inextensible string. The string passes over a frictionless pulley. The body A being heavier must be moving downward with some acceleration. Let this acceleration be a. At the same time, the body B attached to the other end of the string moves up with the same acceleration a. As the pulley is frictionless, hence tension will be the same throughout the string. Let the tension in the string be T.

Question # 8

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 # 9

Define and explain centripetal force

Ans 1: Centripetal force: a force that keeps a body to move in a circular path is called centripetal force
Ans 2: Explanation: Consider a body tied at the end of a string moving with uniform speed in circular path. A body has 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 circle. The string pulls the body pre appendicular o its motion. This pulling force continuously changes the direction of motion and remains towards center of circlewe can conclude the following resultseverybody needs centripetal force to move in a circlecentripetal force is always directed toward the centerit has no component in the direction of motionthis force always acts perpendicular to direction of motion of a Bodydirection of motion of a body at any point moving in a circle can be found out by drawing tangent at that point
Ans 3: Example: consider a stone tied to one end of a string rotating in a circle . The tension in string provides the necessary centripetal force. if string is not strong enough to provide necessary tension, it breaks and the stone move away along the tangent to the circle.Moon revolves around the earth. the gravitational force of earth provides necessary centripetal force

Question # 10

State the Newton's first law of motion & Second law of motion.

Ans 1: Newton first law:
A body continues in its state of rest or of uniform motion in a straight line provided no net force acts on it.
Explanation for rest:
Similarly Newton's first law of motion deals with bodies which are either at rest or moving with uniform speed in straight lineAccording to first law of motion, a body at rest remains at rest provided no net force on it .thispart of the law is true as we observe that objects do not move by themselves unless some moves it.
Explanation for motion:
Similarly a moving object does not stop moving by itself. A ball rolled on a rough ground stops earlier than that rolled on smoothground. It is because rough surface offer greater friction. If there would be no force of oppose the motion of the body would never stop
Newton's Second Law of Motion:
When a net force acts upon a body, it produces as acceleration in the body in the direction of force and the magnitude of acceleration is directlyproportional to the net force and is inversely proportional to the mass of the body.
Mathematical From:
If the force f is acting on the body of mass m then we can write this in the mathematical form is as
a x f _______>(1)
a x 1/m _____> (2)
From (1) and (2) we have
a x F/m
a = Constant x F/m
a = k x F/m
In the above equation according to the international system units if m= 1kg
a = 1ms-²,F= 1N then the value of k will be 1. So the equation can be written as
a=1x F/m
F= ma

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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

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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

Write third law of motoin. explain it with examples

Two masses 26 Kg and 24 kgare attachedto the ends ofstringwhich passes over a frictionless pulley. 26 kg islayingover a smooth horizontal table. 24 N mass is

Explain gun and bullet system using law of conservation of momentum

Explain braking and skidding

Define dynamics, also briefly explain force , inertia and momentum

Explain Newtons second law of motion

Derive relation for tension and acceleration when two bodies moving along vertically

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

Define and explain centripetal force

State the Newton's first law of motion & Second law of motion.

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

Write third law of motoin. explain it with examples

Two masses 26 Kg and 24 kgare attachedto the ends ofstringwhich passes over a frictionless pulley. 26 kg islayingover a smooth horizontal table. 24 N mass is

Explain gun and bullet system using law of conservation of momentum

Explain braking and skidding

Define dynamics, also briefly explain force , inertia and momentum

Explain Newtons second law of motion

Derive relation for tension and acceleration when two bodies moving along vertically

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

Define and explain centripetal force

State the Newton's first law of motion & Second law of motion.

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

Define rolling friction. Also explain why rolling friction is less than sliding friction

Derive relation for tension and acceleration when two bodies moving along vertically

Explain Centripetal force and Drive Fc= mv2/r.

define and explain friction

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

Write note on application of centripetal force

Define centrifugal force and explain it briefly

Define and explain centripetal force

A force of 20 N moves a body with an acceleration of 2ms-² What is the mass.

Define dynamics, also briefly explain force , inertia and momentum

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

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Explain Centripetal force and Drive F_c= mv²/r.