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Question: 1
What is weight?
Answer: 1
1-32Weight: The weight of a body is the force with which it is attracgted toward the centre of the earth. It is denoted by symboel"W"
Mathematical form:
W = m x g
W = wg
Quantity and Unit:
Weight is a vector quantity and its SI unit is newton (N)
Question: 2
State and explain Newton's three laws of motion. Give one example of each.
Answer: 2
2-32Newton's Laws of Motion: Isaa Newton formulated three laws based on the observation about the motion of objects. These laws express the relationship among force, mass and the motion of an objecg which are described below:
Question: 3
Wrie Types of force Contact forces and Non- contact forces.
Answer: 3
3-32Contact Forces: Contact forces are those types of forces which result when the two bodies are physically contact with eah other.
Example: Friction forces , push or pul forces etc. are examples of contact forces. e.g. push a cart or drag a chair on floor etc.
Question: 4
Define Law of conservation of Momentum
Answer: 4
4-32If there is no external force applied to a system of particles then the total momentum of that system remains constnat.
In the absence of an exteanl force of the system must be equal to the final mementum.
Question: 5
Define Friction and Unit of friction.
Answer: 5
5-32Friction: The force which always oppose the motion of one body over another bodyin contact with it is called force of friction.
It is denoted by "f"
Example:
1- The ground and the wheels of a car
2- Water and fish swimming through it
3- A flying cricket ball and air etc.
Quantity and unit:
Friction is a vecor quantity and its SI unti is newton (N)
Question: 6
Define Isolated system.
Answer: 6
6-32Isolated System: An isolated system is a collection of particles that can interact with each other but whose interactions with the environment outside the collection have a negligible effect on their motions.
Question: 7
Newton's second Law of Motion:
Statement: The net force "F" on a body is equal to the product of the boyd's mass "m" and its acceleration "a"
Explanation: Newton's second law of motion establishes a relationship between net force,mass and acceleratin. As we know that greater force applied to a body produces greater acceleration. thus, the acceleraton is directly proportioal go the fore i.e. a aF
Answer: 7
7-32Now if the same amount of force is appied to differnet masses, it will produce different acceleration. A heavier body willacquire lesser acceleration than a lighter body. This means that the acceleration is inversaly proportionalto the mass of body.
Mathmatically form= F = ma
Question: 8
Write Newton's Third Law of Motion
Answer: 8
8-32Statement: " To every action there is always an equal and opposite reaction".
Explanation: According to Newton's third law of motion, when one object exerts a force on a second object, the second object exerts a force of the same magnitude and opposite direction on the first object. So, whne an object "A" exert force on object B written as FAB, object "B" also exert equal force on object A written as FBa but in opposite directin. i.e.
F AB = - FBA
Question: 9
Define Momentum.
Answer: 9
9-32The quantity of motion in a body is called memnetum.
Quantity and unit:
Momentum is a vector quantity where its direction is same as that of velocity of the body and the SI unit of momentum is kilogrma meter per second or Newton-second.
Question: 10
Define collision and explosion.
Answer: 10
10-32Collision: An event during which particles ome close to each other and interact by mean of forces is called collision
Question: 11
Difference between Mass and Weight.
Answer: 11
11-32Mass:
The quantity of matter in a body is called mass
Mass denoted by "m"
The S.I unit of mass is kilogram
Mass is a scalar quantity beacuse it has no direction
Mass can be measured by beam balance
Mass can be found by formula: m = F/a
Mass cannot be zero
Mass is the measure of inertia.
Question: 12
What is force?
Answer: 12
12-32Definition: Force is a physical quantity whcih moves or tends to move a body, stops or tends to stop a moving body or which tends to change the speed and directions of a moving body.
Question: 13
What is uniform circular motion ?
Answer: 13
13-32Uniform circular motion: " If a body moves in a circular path with a uniform speed, its motion is called uniform ircular motion."
Example:
1- Motion of earth around the sun.
2- Motion of electrons around the nucleus
3- Motion of fan etc.
Question: 14
What are the advantages and Disadvantages of friction ? Also give methods to reduce and improve friction.
Answer: 14
14-32Advantages of frcition.
1- We can walk on the ground with the help of friction between the soles of our shoes and the ground.
2- The nails remain fixed in the walls and wood due to friction.
3- The lighting of a match stic is another useful applicationof friction.
4- The moving vechicles can be stopped by applying brakes due to friction.
5- Friction enable us to writ eon paper.
Question: 15
Define Co-efficient of static friction and Co-efficient of kInetic friction.
Answer: 15
15-32Co-efficient of Stati friction:
As we know that, the static friction "fs" is directly proportional to the normal force "FN" ACTING ON THE BODY I.E.
Fs = meos FN
Where "meos" is a constant of proportionaity kknown as the coefficient of stati friction and depends on the nature of surfaces in contact before sliding.
Question: 16
Define Centrifuge.
Answer: 16
16-32Centrifuge is a device which is used for the separaion of liquids of unequal densities. Its operaion depends upon centripetal force.
Construction nd working: A simplest type of centrifuge consists of a wheel which rotates horizontally and some bucketsare attached to the wheel vertically. Now, if a mixture of unequal densities are introduced into the buckets and the wheel is allowed to rotaate rapidly. the liquid becomes separate tha tis the heavy liquid remains farther from the azis of rotation while the ligher liquids remains nearer to it.
Example: The same centrifuge Principle can be used in some commonly used devices in our daily life. i.e. cream separator and washing machine dryer are teh examples of centrifuge.
Question: 17
Define and explain centripetal force.
Answer: 17
17-32Centripetal force: The force which compels a body to move in a circle is called centripetalforce. It is denoted by 'Fc'.
Explanation: We know that in circular motion, the direction of velocity of body change continuously. Thus, acceleration is produced during such motion. The force required for the production of centripetal acceleration is known as centripetal force and it is always directed towards the centre of circle. In the absence of centripetal force. the object will travel in a straight line. Hene, the effect of centripetal force is to contnuously change the direction of moving object, forcing it to move in a circle.
Question: 18
Define Baking of Road.
Answer: 18
18-32To make the outer edge of a curved road is a little highe rthan the its inner edge is known as baking of road.
When a car takes as turn along a round track, sufficient centripetal force is required. In the absence of this force. The car will skid off the road provides this centripetal force and keeps the car moving on the curved path. However, if the road is slippery due to rain or snow, this reduces the friction which in turn reduces centripetal force of taking turn.
Question: 19
What is Tension
Answer: 19
19-32Tension: The pulling fore exerted by a stretched rope, string or cable on an object to which it is attached is called a tension fore. It is denoted by "T"
Question: 20
What is Atwood's machine.
Answer: 20
20-32Consider, motion of two bodies A" and "B" having masses m1 and m2 are suspended by an extensible strig whihc passes over a srictionless pully. Such arrangement is known as simplified Atwood's machine.
Question: 21
What is centripetal force?
Answer: 21
21-32CENTRIPETAL FORCE: The force which compels a body tomove in a circular path is called centripetal force. It is denoted by "Fc"
Mathematical forme:
Fc= mv2/r
Where "m" is the mass of the body, "v"is the velocity of the body and "r"is the radius of the circle.
Question: 22
Describe various type of friction.
Answer: 22
22-32Types of friction: There are two types of frictional forces which are given below.
1- Sliding friction 2- Rolling friction
Question: 23
Define Centripetal acceleration.
Answer: 23
23-32The acceleration which is produced by changing the directio of motion of a body moving in a circular path with constnat speed is called centripetal acceleration. It is denoted by "ac".
Explanation: We know that during the circular motion the direction of velocity of the body changes at every point continuously due to which an acceleration is produced which is known as centripetal acceleration.
Question: 24
Differentiate between Static and Kinetic friction by giving an example.
Answer: 24
24-32Static Friction: The maximum force of friction that is opposite to the applied force and prevents the body from moving is called static friction. It is denoted by "f"
Mathematical form:
fx = meo s FN
Kinetic Friction :
The force of friction that acts against during motion of an object in a direction opposite to the direction of motion is called kinetic friction. It is denotedby "fk"
Mathematical form:
fk = meo k FN
Example:
1- The weight "W" of the body is acting downward.
2- The normal force "FN" which is acting upward
3- The applied force "F"
4- The force of static friction "fx" which is acting in opposite direction to the applied force as shown in figue A.
Question: 25
How does friction hep you walk? Is it kinetic frictionor static friction?
Answer: 25
25-32A frincional force exists between the ground and sole of our shoes. When we walk forward, we push the ground with feet in the backward diretion while in reaction, the ground also exets a force in forward direction which moves us forward. Because of this frictional force, we are able to walk on the ground. Without friction, it is not possible for us to walk on the ground this is Static Friction because when we walk on the ground, our feet are at rest for a moment which privides the static friction between our feet and ground. Hene, we walk due to static fricton instead of kinetic friction.
Question: 26
Why does dust fly off, when a hanging carpet is beaten with a stick?
Answer: 26
26-32When we beat a carpet with a stick, the carpet is set into motion while the dust particles inside the carpet are at rest and tends to remain at rest due to inertia. As the dust particles do not move with the carpte, so they got removed from the carpet.
Question: 27
Write a note on ws=ashing machine dryer.
Answer: 27
27-32Washing machine dryer: A washing machine dryer is a device which is used to dry the wet clothes quickly. It works on the principle of contrifuge.
Construction: It consists of a cylinder having small hles on its wall and a rotor which is driven by an electric motor.
Working: When wet clothes are placed in this cylinder and it is rotated rapidly. Due to this, water moves outward to the wall of cylinder and is drained out through the holes. In this way the clothes become dry quickly.
Question: 28
Why a ballon filled with air move forward when its air is released?
Answer: 28
28-32When air is released from ballon, the ballon exerts an action force on the air and pushes it out in the backward direction. While the rushing out air exerts an equal reaction force on the ballon in forward direction. As a result, the baloon moves forward.
We can also explain this in tems of the law of conservatin of momentum. The air and baloon form an isolated system whose gtotal momentum is initially zero. Now, when air is released, it rushes out with great momentum in the back ward direcion. Now to conserve the momentum, the balloon moves forward with same momentum.
Question: 29
In uniform circular motion, is the velocity constnat? Is the acceleration constnat? Explain
Answer: 29
29-32In uniform circular motion, the velociy does, not remain constnat because the directin of velocity of the obdy change continuously from point to pont and this direction of velocity is always tangent to circle at each point. Wheas, the centripetal acceleration is directed towards the centre of circular path and its dircation remain unchnged. Due to uniform circular motion, the centripetal acceleration remains constant throughout the motion.
Question: 30
If your hands are wet and no towel is handy,you can remove some of the excess water by shaking them, why does this work?
Answer: 30
30-32We can remove some of the excess water from our wet hands by shaking them due to inertia when we shake our hands, the hands come into state of motion while the drops of water are at rest and tend to remain at rest due to intertia. As a result, these drops are remove rom our hands.
Question: 31
Why does a boatman tie his boat to a pillar before allowing the passengers to step on the river bank?
Answer: 31
31-32When the passengers jumps from the boat on the river bank, they actualy push the boat with their feet in the backwrd direction IN this way, the boad would move away from the bank and the passengers may fal in water, So, to avoid the baceward push of the boat. It is first tied to he pillar before allowing the passenger to step on the river bank.
Question: 32
Write a note on cream separator.
Answer: 32
32-32CREAM SEPARATOR: A cream separator is a centrifugal devie which is used to separate cream from milk. It works on the principle of centrifuge.
Construction: It consists of a set of blades connected to an axis by means of a metallic rod which is driven by an electric moter.
Working: As milk is a mixture of light and heavy particles, the turning blades of this device spins the milk due to which the light and heavy particles of milk are separated. The light particles gather near the axis of rotation while the heay partcles of milk go away from the axis of rotation in this way cream is separated from milk
