Question

33. Kepler's third law of motion implies that..

A. planets move around the sun in elliptical orbits.
B. planets orbiting further away from the sun move faster than inner planets.
C. planets approaching the sun have larger average speed than when they are further away from the sun.
D. planets orbiting further away from the sun move slower than inner planets.

Answer 1

Kepler’s three laws of planetary motion can be stated as follows:
(1) All planets move about the Sun in elliptical orbits, having the Sun as one of the foci.
(2) A radius vector joining any planet to the Sun sweeps out equal areas in equal lengths of time.
(3) The squares of the sidereal periods (of revolution) of the planets are directly proportional to the cubes of their mean distances from the Sun.

If we want to elaborate the 3rd law, it means The square of the orbital period of a planet is proportional to the cube of the semi major axis of the ellipse. Means the planet which is away from the Sun will take more time to cover same distance ... means planet which is near to the sun has higher speed or we can say that PLANETS ORBITING FURTHER AWAY FROM THE SUN MOVE SLOWER THAN INNER PLANETS MEANS OPTION D IS CORRECT.