Question
One year at a planet is 8 times as large as compared to the one year at the Earth. Which one of the following is correct about the planet's orbit?
NDA
General Ability
General Science
2026
NDA 2026 (Phase 1)
NDA General Ability Question (2026) — Solution
Options
- A. The semimajor axis of the planet's orbit is same as that of the Earth.
- B. The semimajor axis of the planet's orbit is twice as compared to that of the Earth.
- C. The semimajor axis of the planet's orbit is thrice as compared to that of the Earth.
- D. The semimajor axis of the planet's orbit is four times as compared to that of the Earth.
Answer
D. The semimajor axis of the planet's orbit is four times as compared to that of the Earth.
Step-by-step solution
According to Kepler's third law of planetary motion, the square of the time period of revolution is directly proportional to the cube of the semimajor axis of the orbit. T^2 a^3 ( T_p T_e )^2 = ( a_p a_e )^3 Given that T_p = 8 T_e, substituting this value: (8)^2 = ( a_p a_e )^3 64 = ( a_p a_e )^3 a_p a_e = (64)^ 1/3 = 4 a_p = 4 a_e The semimajor axis of the planet's orbit is four times as compared to that of the Earth. Answer: The semimajor axis of the planet's orbit is four times as compared to that of the Earth.
Related: General Ability — General Science · All PYQ Banks