Class 9th Physics Chapter 5 Question Answer

Complete Notes of Class 9th Physics Chapter 5 Question Answer Gravitation Numericals of 9th Class Physics Urdu Medium written by Sir Fahad Abbas Suib. These computerized notes are very helpful in the preparation of Gravitation Numericals Class 9 for students of the Class 9th Physics Chapter 5 Question Answer these are according to the paper patterns of all Punjab boards.

• Important Values and Important Formulas
• Gravitation Exercise Numericals with Solutions in Urdu 
• Law of gravitation and newton's third law of motion class 9: It is to be noted that mass m attracts m towards it with a force F while mass m attracts m towards it with a force of the same magnitude F but in opposite direction. If the force acting on m is considered as action then the force acting on m will be the reaction. The action and reaction due to force of gravitation are equal in magnitude but opposite in direction. This is consistent with Newton's third law of motion which states, to every action there is always an equal but opposite reaction.
• Gravitational field class 9: According to the Newton's law of gravitation, the gravitational force between a body of mass m and the Earth is given by   F = G mMe/r^2   where M is the mass of the Earth and r is the e distance of the body from the centre of the Earth. The weight of a body is due to the gravitational force with which the Earth attracts a body. Gravitational force is a non-contact force. Such a force is called the field force. It is assumed that a gravitational field exists all around the Earth. This field is directed towards the centre of the Earth. The gravitational field becomes weaker and weaker as we go farther and farther away from the Earth. In the gravitational field of the Earth, the gravitational force per unit mass is called gravitational field strength of the Earth. Gravitational field Strength Class 9 At any place its value is equal to the value of g at that point. Near the surface of the Earth, the gravitational field strength is 10 N kg^-1.
• MASS OF THE EARTH CLASS 9: Consider a body of mass m on the surface of the Earth. Let the mass of the Earth be M and radius of the Earth be R. The distance of the body e from the centre of the Earth will also be equal to the radius R of the Earth. According to the law of gravitation,
• Variation of g with altitude class 9: The value of acceleration due to gravity g depends on the radius of the Earth at its surface. The value of g is inversely proportional to the square of the radius of the Earth. But it does not remain constant. It decreases with altitude. Altitude is the height of an object or place above sea level. The value of g is greater at sea level than at the hills. Consider a body of mass m at an altitude h. The distance of the body from the centre of the Earth becomes R + h. Therefore,
• Artificial satellites class 9: An object that revolves around a planet is called a satellite. The moon revolves around the Earth so moon is a natural satellite of the Earth. Scientists have sent many objects into space. Some of these objects revolve around the Earth. These are called artificial satellites. Most of the artificial satellites, orbiting around the Earth are used for communication purposes. Artificial satellites carry instruments or passengers to perform experiments in space.
• Large number of artificial satellites have been launched in different orbits around the Earth. They take different time to complete their one revolution around the Earth depending upon their distance h from the Earth. Communication satellites take 24 hours to complete their one revolution around the Earth. As Earth also completes its one rotation about its axis in 24 hours, hence, these communication satellites appear to be stationary with respect to Earth. It is due to this reason that the orbit of such a satellite is called geostationary orbit. 
• The height of a geostationary satellite is about 42,300 km from the surface of the Earth. Its velocity with respect to Earth is zero. 
• Global Positioning System (GPS) is a satellites navigation system. It helps us to find the exact position of an object anywhere on the land, on the sea or in the air. GPS consists of 24 Earth satellites. These satellites revolve around the Earth twice a day with a speed of 3.87 km s^-1.