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1. If a spacecraft has to be sent away from the influence of the earth’s gravitational field, its velocity must be less than the escape velocity. State with reason, whether this sentence is true or false.
Answer: False. The spacecraft needs to escape the earth’s gravitational force so that they can travel into outer space. To achieve this, the initial velocity of the moving object has to be greater than the escape velocity of the earth.
2. What is meant by an artificial satellite? How are the satellites classified based on their functions?
Answer: An astronomical object revolving around the earth or any other planet is the natural satellite. Similarly, an artificial satellite is the man-made object that orbits around the earth or another planet in a fixed orbit. Meanwhile, as per their functions, satellites are classified into following categories:
3. Suppose the orbit of a satellite is exactly 35780 km above the earth’s surface. Determine the tangential velocity of the satellite.
Answer: Here, G is 6.67 × 10-11 N m2 /kg2 ,
M is given as 6×1024 kg (for earth)
R = 6400 km (for earth) = 6.4 × 106 m ,
h is the height of the satellite above the earth’s surface = 35780 km.
So, what is v =?
Given that R + h = 6400 + 35780 = 42180 × 103 m
Use the formula, v = √GM/(R+h)
Replacing with values, you get
v= √[(6.67 × 10-11 ) ×(6×1024 ) / 42180 × 103 ]
v= √[40.02 x 1013 / 42180 x 103 ]
= √0.0009487909 × 1010 = √ 9487909
So, v= 3080.245 m/s = 3.08 km/s
4. Explain some uses of communication by satellite.
Answer: During the war, satellites were used to get information about the actions of the enemy through aerial surveillance. It was also used to explore the fossil reserves and minerals in the earth.
5. What are geosynchronous satellites?
Answer: Earth takes almost 24 hrs for one revolution. In case the satellite is revolving in an orbit parallel to the equator, the time of the revolution of the surrounding earth will be the same as that for the satellite to revolve around the earth. Hence, the satellite will appear to be stationary with respect to the earth. For a passenger in one vehicle, another vehicle, moving parallel to him with equal velocity, appears to be stationary. This is the same as that. These satellites are, therefore, called geosynchronous satellites.
6. How long does it take for us to reach the moon?
Answer: Moon is an astronomical object placed closest to us. It is seen that light takes 1s to reach from the moon to the earth. Hence, if we travel with the speed of light, it will take 1s to reach the moon. However, a spacecraft travels at much lower speed, so it takes longer to reach the moon. The Shortest time ever taken by a spacecraft to reach the moon, till date is 8 hours and 36 minutes.
7. Why is it essential to manage the debris found in space?
Answer: Apart from the artificial satellite, there are some other objects also orbiting around the earth. These objects are non-functional satellites, parts of the launcher detached during launching and the debris that is generated due to collision of satellite with other satellite or any other object in the space. These debris can harm the artificial satellites. These can damage the spacecraft or satellites when it collides with them. So, it is very essential to manage the debris.
8. Which is the first artificial satellite?
Answer: ‘Sputnik’ is the first artificial satellite. The Soviet Union sent this satellite into space in 1957.