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Question
Will the angular momentum of a planet be conserved? Justify your answer.
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Solution
The torque experienced by the Earth due to the gravitational force of the Sun is given by,
`vecτ = vec"r" xx vec"F" = vec"r" xx (-("GM"_"S""M"_"E")/"r"^2 hat"r") = 0`
Since `vec"r" = "r", hat"r", (hat"r" xx hat"r") = 0`
So `vecτ = ("d" vec"L")/"dt" = 0`
It implies that angular momentum `vec"L"` is a constant vector. Hence L is conserved.
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