Answer
Centrifugal force
Consider a stone tied to a string moving in a circle. The necessary centripetal force acts on the stone through the string that keeps it to move in a circle. According to Newton's third law of motion
There exists a reaction to this centripetal force. Centripetal reaction that pulls the string outward is sometimes called the centrifugal force
Banking of road
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 a road means that the outer edge of 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 makes the driving safe
Q. Define and explain the moment of inertia?
Answer
Moment of Inertia (Rotational Inertia)
The tendency of a body to maintain its state of rest or state of uniform angular motion is called moment of inertia
OR
It is defined as the product of mass of particle and square of its perpendicular distance from the axis of rotation
It is denoted by I and is given by
mr OR
The sum of products of masses of the particles in a body and the square of their respective distance from the axis of rotation is called moment of inertia
Rotational Kinetic Energy
The energy possessed by the body due to its rotation about an axis is called rotational kinetic energy
Expression for rotational K.E
Suppose the body is spinning or rotating about an axis with constant velocity In order to find the total KE of spinning body, we consider that it is composed of small pieces of masses m.mUse of rotational K.E.
Rotational KE. is put to practical use by fly wheels, which are essential parts of many engines. A fly wheel stores energy between the power strokes of the pistons, so that energy is uniformly distributed over the full revolution of the crank shaft and hence, the rotation remains smooth
Q. Explain the phenomenon of weightless in satellites and gravity free system.
Answer
Weightlessness in Satellite and Gravity Free System
When a satellite is falling freely in space under the action of force of attraction of earth, the sun or some distance star then the everything within the satellite will be in state of weightlessness To show that the earth's satellite is a freely falling object, we consider the behavior of projectile thrown parallel to horizontal surface of the earth in the absence of air friction If the projectile is thrown successively larger speeds, then during its free fall to the earth, the curvature of the path decreases with increasing horizontal speeds it the projectile is thrown fast enough parallel to the earth The curvature of the path will match the curvature of the earth.
There is no force on the space craft in a gravity free space If the spaceship is to stay in the orbit for a longer time, this weightlessness creates a lot of problems for astronauts present in the spaceship To overcome this difficulty, an artificial gravity is created in the spaceship to perform the experiments normally by astronauts
The astronaut then is pressed towards the outer nm and exerts a force on the floor of spaceship in much the same way as on the earth
Q. What are geo-stationary orbits and geostationary satellite? Find the orbital radius of geo stationary satellites?
Answer
Geostationary orbits
The orbit in which the period of revolution of satellite is exactly equal to the period of rotation of earth about its axis, is called geostationary orbit
Geostationary satellites
The satellite which complete its one resolution around the earth in 24 hours is called geostationary satellite
An interesting and useful example of satellite motion is the geo synchronous or geostationary satellite This type of satellite is the one whose orbital motion becomes equal to the period of rotation of earth. So the satellite remains always over the same point on the equator as the earth spins on its axis Such satellites are used in communication system weather observation and other military uses
Q. Write a short note on communication satellite?
Answer
Communication satellites
A communication satellite system can be set up by placing several geostationary satellite in orbit over different point on the surface of earth such a satellite we covers 120" of longitude So the whole of the populated earth's surface can be covered by three correctly positioned satellites Use of waves for communication
Microwaves are used in communication network because they travel in a narrow beam, in straight line and can pass easily through atmosphere of the earth
Solar cells provide the energy to amplify and re-transmit the signal About 200 earth stations transmit and receive the signals via satellite from other countries
Satellite Organization (INTELSAT)
The largest satellite system, managed by 126 countries is called INTELSAT VI INTELSAT means international telecommunication satellite organization it works at the microwave frequencies of 4 6 11 and 14 GHz and has the capacity of 30 000 two way telephone circuit plus three TV channels
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