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

Question # 1

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 # 2

Write note on application of centripetal force

Ans 1: There are many application of centripetal force but some are following
Ans 2: Banking of roads: when a car takes a turn, centripetal force is needed to keep it in its curved track. The friction between the tyres and the road provides the necessary centripetal force. the car would skid if the force of friction between the tyres and the road is not sufficient enough, particularly when the roads are wet. This problem is solved by banking of curved roads . Banking of road means that the outer edge o a road is raised . Imagine a vehicle on a curved road. banking causes a component of vehicles weight to provide the necessary centripetal force while taking a turn. Thus banking of roads prevents skidding of vehicle and thus the deinking safe
Ans 3: Washing machine dryer; the dryer of a washing machine is basket spinners. They have a perforated wall having large numbers of fine holes in the cylindrical rotor. The lid of the cylindrical container is closed after putting wet clothes in it. When it spins at high speed, the water from wet clothes is forced out thorough these holes due to lack of centripetal force
Ans 4: Cream: separator: most modern plants use a separator to control the fat contents of various products. A separator is a high speed spinner. it acts on the same principle of centrifuge machines. The bowl spins at very high sped causing the heavier contents of milk move outward in the bowl pushing the lighter contents inward towards the spinning axis. Cream or butterfat is lighter than other components in milk. Therefore, skimmed milk. which is denser than cream is collected at the outer wall of the bowl. The lighter part ( cream0 is pushed toward the center from where it is collected thorough a pipe.

Question # 3

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 # 4

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

Ans 1: F = 20 N
a= 2ms-²
m=?
Solution:
F=ma
So m= 20/2
m = 10 kg

Question # 5

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 # 6

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 # 7

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

Ans 1: Rolling friction: force of friction between body and surface when a body rolls over a surface e.g. when a wheel rolls on ground
Ans 2: Sliding friction: force of friction between body and surface when a body slides over a surface. when a wooden block moves over asurface of table then the force friction between block and surface of table is sliding friction
Ans 3: Comparison of rolling and sliding friction: rolling friction is less than sliding friction because in rolling friction a body rolls without rupturing the cold welds , while in sliding friction a body slides' by rupturing the cold welds so sliding friction is more than rolling friction

Question # 8

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 # 9

Write differences between mass and weight

Ans 1: Mass: Mass o a body is the quantity of matter possessed by the bodyits a scaler quantityit is measured by using a common balance( beam balance)it remains same everywherethe SI unit of mas is kilogram(kg)it is a base quantity
Ans 2: Weight: weight of a body is the force of gravity acting on itit is a vector quantityit is measured by using a spring balanceit varies depending upon the value of acceleration due to gravity gthe SI unit of weight is newton(N)it is a derived quantity

Question # 10

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

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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

Define and explain centripetal force

Write note on application of centripetal force

define and explain friction

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

Explain Newtons second law of motion

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

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

Write third law of motoin. explain it with examples

Write differences between mass and weight

Explain law of conservation of momentum

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

Define and explain centripetal force

Write note on application of centripetal force

define and explain friction

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

Explain Newtons second law of motion

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

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

Write third law of motoin. explain it with examples

Write differences between mass and weight

Explain law of conservation of momentum

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

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

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

Write note on application of centripetal force

define and explain friction

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

Explain law of conservation of momentum

Explain Centripetal force and Drive Fc= mv2/r.

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

Define centrifugal force and explain it briefly

Explain Newtons second law of motion

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

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Explain Centripetal force and Drive F_c= mv²/r.