Question

Which of the following statements are true?

• A. Only (i) and (ii)
• B. Only (ii) and (iii)
• C. Only (i) and (iii)
• D. (i), (ii) and (iii)

Answer 1

The correct option is A

Only (i) and (ii)

Kepler's laws of planetary motion:

1. The law of Orbits: Every planet moves around the sun in an elliptical orbit with the sun at one of the foci.
2. The law of Area: The line joining the sun to the planet sweeps out equal areas in equal interval of time that is area velocity is constant.
3. As per this law the planet will move slowly when it is farthest from the sun and more rapidly when it is nearest to the sun. It is similar to the law of conservation of angular momentum.
4. The law of Periods: The square of the period of revolution (T) of any planet around the sun is directly proportional to the cube of semi-major axis of the orbit that is $T^2\propto r^3$.
5. Thus, it is clear that every planet moves around the sun in an elliptical orbit with the sun at one of the foci. Therefore, statement (i) is correct.
6. The line joining the sun to the planet sweeps out equal areas in equal intervals of time that is area velocity is constant. Therefore, statement (ii) is correct.
7. The square of the period of revolution (T) of any planet around the sun is directly proportional to the cube of semi-major axis of the orbit. Therefore, statement (iii) is incorrect.

Hence, option (A) is correct.