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Subject :NSO    Class : Class 9

Kepler's third law states that square of period of revolution (T) of a planet around the sun is proportional to third power of average distance r between the sun and the planet i.e. T2 = Kr3 (here K is constant). If the masses of sun and planet are M and m respectively then as per Newton's law of gravitation, force of attraction between them is F = GMm/r2, here G is gravitational constant.
The relation between G and K is described as

A K = G
B K = 1/G
C GK = 4π2
D GMK = 4π2

Ans 1:

Class : Class 9
Correct ans:D. The gravitational force is equal to the centripetal force acting between the Sun and Planet. GMm/r^2=Mv^2/r =>v^2=Gm/r. Also,T=2(pi)r/v. Squaring both the sides we will get

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