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Question 8.3:
Suppose there existed a planet that went around the sun twice as fast as the earth.What would be its orbital size as compared to that of the earth?
Lesser by a factor of 0.63
Time taken by the Earth to complete one revolution around the Sun,
Te = 1 year
Orbital radius of the Earth in its orbit, Re = 1 AU
Time taken by the planet to complete one revolution around the Sun, 
Orbital radius of the planet = Rp
From Kepler’s third law of planetary motion, we can write:
Hence, the orbital radius of the planet will be 0.63 times smaller than that of the Earth.
