Practice question
Question
A planet orbits the Sun with a period of 5 years. If Earth’s orbital radius is 1.5×1011m, what is its semi-major axis?
Explanation
Kepler’s third law: Tp2TE2 = ap3aE3. TE = 1year, Tp = 5years, aE = 1.5×1011m. 5212 = ap3(1.5×1011)3. 25 = ap33.375×1033. ap3 = 25×3.375×1033 = 8.4375×1034. ap = (8.4375×1034)1/3≈4.39×1011m. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 4.4 × 10¹¹ m. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.