Question

According to Kepler’s III law of planetary motion, __________ . (T = time period, R = Radius of the orbit)

• A. $T\alpha R$
• B. $T^2\alpha R^3$
• C. $T^3\alpha R^2$
• D. $T^{}\alpha R^3$

Answer 1

The correct option is B

$T^2\alpha R^3$

According to the observation of the Kepler different planets takes different time to complete the one revolution around the sun. On the basis of this observation, Kepler gave three laws -

First law

According to Kepler's first law planets revolve around the sun in elliptical orbits and the sun is at one of its foci.

Second law

According to Kepler's second law line joining the planet to the sun sweeps over an equal area in equal intervals of time. It means that planets move faster when they are close to the sun.

Third law

The third law of Kepler gives the relation between the time period and distance of the planet from the sun. $T^2\alpha r^3$

Hence the correct option is (B) .