Question

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Question : name the physical quantities which remain constant during the planetary motion.

Answer 1

According to Kepler's second law of planetary motion, areal velocity ( area swept by the line joining the sun with the planet per unit time) is constant. This law is equivalent to law of conservation of angular momentum.

Areal velocity for circular orbit is given by r^2w/2.

Multiplying by mass m of the planet, we have,

m r^2w /2.

But, mr^2w= angular momentum, L.

Therefore, areal velocity = L/(2m).