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Chapter 5 Circular Motion Physics 11th Class Punjab Short Questions

Question No. 1 - What is Geo-stationary satellite? How many minimum number of Geo-stationary satellites are required fro global coverage coverage of T.V transmission?

Answer No. 1 - S satellite whose orbital motion is stationary along the earth is called geostationary satellite. The time period of satellite is equal to the time period of spin motion of the earth.
A geostationary satellite covers 120° of longitude. So the whole earth can be covered by three correctly positioned Geo-stationary satellites.

Question No. 2 - What are Artificial Satellites?

Answer No. 2 - Artificial Satellites are the man-made objects that orbit around the Earth.

Question No. 3 - Write down application of communication satellites.

Answer No. 3 - A satellite communication system consist of three Geo-stationary satellites.There are over 200 Earth stations which can transmit and receive signals.INTELSAT-VI operates at microwave frequencies 4, 4, 11 and 14 Ghz and has a capacity of 30,000 two way telephone circuits plus three TV channels.
Geo-stationary satellite are very useful for worldwide communication,weather observation, navigation, and other military uses.

Question No. 4 - Why banked tracks are needed for turns?

Answer No. 4 - Banked tracks are needed because friction alone cannot provide energy for centripetal force.
If the road is banked, so that the outer edge is above the inner edge, then a portion of the normal force from the road on the Tyre points towards the center of the track; this fraction of the normal force can provide enough centripetal force to keep the car moving in a circle.

Question No. 5 - Explain why earth's satellite despite of being freely falling object does not reach the earth.

Answer No. 5 - To orbit the planet and not come crashing down, a spacecraft has to travel forward (tangential to Earth ) fast enough that it compensates for the fall downwards. The trajectory of its fall has the same curvature as earth's surface. So it will never reach the earth.

Question No. 6 - How would you determine the direction of angular momentum?

Answer No. 6 - The direction of angular momentum can be determined by right hand rule:
"Grasp the axis of rotation in right hand with the figures curling in the direction rotation then the erect thumb will give the direction of angular momentum."

Question No. 7 - Why the microwaves are used in satellite communication?

Answer No. 7 - Micro waves are used in satellite communication because they travel in a narrow beam, in a straight line and pass easily through the atmosphere of the earth.

Question No. 8 - When mud files off the Tyre of a moving bicycle, I what direction does it fly?

Answer No. 8 - Adhesive force between mud and tire is weal. When the mud files off the Tyre of a moving bicycle, it always files along the tangent to the Tyre. Because linear velocity is always tangent to the circle.

Question No. 9 - State the direction of the following vectors in simple situation: A) Angular Momentum B) Angular Velocity

Answer No. 9 - The direction of angular momentum and angular velocity can be determined by right hand rule;
"Grasp the axis of rotation in right hand with the figures curling in the direction of rotation, then the erect thumb will give the direction of angular velocity and angular momentum."

Question No. 10 - Define angular velocity give its units and dimensions.

Answer No. 10 - The rate of change of angular displacement is called angular velocity. The direction of angular velocity is along the axis of rotations of the body.
S.I unit of angular velocity = rad/s
Dimensions of angular velocity = [T-1]

Question No. 11 - What are geostationary orbit and geostationary satellites?

Answer No. 11 - Geostationary Orbit: An orbit in which the time period of satellite is equal to the time period of spin motion of the earth is called geostationary orbit.

Geostationary Satellites: A satellite whose orbital motion is stationary along the earth is called geostationary satellite.

Question No. 12 - On what factors moment of inertia depends?

Answer No. 12 - The moment of inertia is I =mr2
So it depends upon the mass of the body and its distance from the axis of rotation.

Question No. 13 - How is artificial gravity created?

Answer No. 13 - Artificial gravity is the gravity like effect produced in an orbiting spaceship to overcome weightlessness.To create artificial gravity the spaceship is set into rotation around its own axis. The astronaut then is presses towards the outer rim and exerts a force on the floor of the spaceship in much the same way as on the earth.

Question No. 14 - Why is the axis of rotation of Earth remains fixed in one direction with respect to the universe around it?

Answer No. 14 - The major force acting on Earth is the pull of the Sun and no other sizable toque is experienced by it. The Earth's axis of rotation, therefore remains fixed in one direction with reference to the universe around us.

Question No. 15 - Explain the difference between tangential velocity and angular velocity.

Answer No. 15 - The linear velocity of a particle moving along a curve or circle is called tangential velocity. Its direction is always along the tangent to the circle.
The rate of change of angular displacement is called angular velocity.The direction of angular velocity is along the axis of rotation of the body by right hand rule. V= rw

Question No. 16 - Define angular velocity, How its direction is determined?

Answer No. 16 - The rate of change of angular displacement is called angular velocity. The direction of angular velocity is along the axis of rotation and can be determined by right hand rule:
"Grasp the axis of rotation in right hand with the figures curling in the direction of rotation then the erect thumb will give the direction of angular velocity."

Question No. 17 - Why Einstein views of gravitation are preferred than Newton's views of gravitation? Explain briefly.

Answer No. 17 - Newton discovered the inverse square law of gravity. Einstein's theory also says that gravity follows an inverse square law (except in strong gravitational fields), but it gives us a physical picture of how gravity works. The bending of star light caused by the gravity of the Sun was measured during a solar eclipse in 1919, it was found to match Einstein's Prediction rather than Newton's.

Question No. 18 - What is meant by INTEL SAT? At what frequencies the INTELSAT-VI operates?

Answer No. 18 - The largest satellite system managed by 126 countries is international. Telecommunication Satellite Organization (INTELSAT).
The INTELSAT-VI operates at microwaves frequencies of 4, 6, 11 and 14 Ghz.

Question No. 19 - Why you wear seat belts?

Answer No. 19 - During collision, the passengers move forward towards the windscreen due to inertia. The seat belt prevents the passenger from moving forward. And lessened the chances of injury.

Question No. 20 - What is meant by moment of inertia? Explain its significance.

Answer No. 20 - The product of mass of the particle and square of its perpendicular distance from the axis of rotation is called the moment of inertia.

I =mr2
The moment of inertia plays the same role in angular motion as the mass in linear motion.

Question No. 21 - What are Artificial Satellites and how they move around the earth?

Answer No. 21 - Satellites are the objects that orbit around the earth.They are put into orbit by rockets and are held in orbits by the gravitational pull of the earth.

Question No. 22 - Define Moment of Inertia. Write its formula.

Answer No. 22 - The property of the body to resist any change in its state of rest or uniform angular velocity is called moment of inertia. For a point mass 'm'situated at a distance 'r' from the axis of rotation , the moment of inertia 'I' is given by ; I=mr2
Significance;
Moment of inertia plays the same role in angular motion as that of mass plays in linear motion. It is also called measure of rotational inertia in angular motion.Moment of inertia determines the angular acceleration while mass determines the linear acceleration.

Question No. 23 - An object orbiting around the earth in said to be a freely falling body. Why?

Answer No. 23 - An object in orbits is said to be freely falling , because the trajectory of its fall has the same curvature as Earth's surface. In fact, the object is falling towards the center of earth but because of spherical shape of earth, it never reaches the surface of earth.

Question No. 24 - Explain how many minimum number of Geo-stationary satellites are required for global coverage of T.V transmission.

Answer No. 24 - A geostationary satellite covers 120° of longitude. So the whole earth can be covered by three correctly positioned geostationary satellites.

Question No. 25 - Explain conservation of direction of angular momentum.

Answer No. 25 - The direction of angular momentum along the axis of rotation remains fixed. This is due to the fact that the axis of rotation of an object will not change its orientation unless an external torque causes it to do so.

Question No. 26 - Define centripetal force and centripetal acceleration.

Answer No. 26 - The force needed to bend the normally straight path of the particle into a circular path is called the centripetal force.
The instantaneous acceleration of an object traveling with uniform speed in a circle is directed towards the centre of the circle and is called centripetal acceleration.

Question No. 27 - State the right hand rule to find the direction of angular displacement.

Answer No. 27 - It states that
"Grasp the axis of rotation in right hand with the fingers curling in the direction of rotation , then the erect thumb will give the direction of angular velocity and angular momentum"

Chapter 5 Circular Motion Physics 11th Class Punjab Short Questions

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