Q. When a uniform solid sphere and a disc of the same mass and of the same radius rolls down an inclined smooth plane from rest to the same distance, then the ratio of the time taken by them is

A) 15 : 14
B) $15^{2}:14^{2}$
C) $\sqrt{14}\ :\sqrt{15}$
D) 14 : 15
Explanation

(c) $t = \frac{1}{\sin\theta}\sqrt{\frac{2h}{g}\left( 1 + \frac{K^{2}}{R^{2}} \right)}$
$\Rightarrow \frac{t_{S}}{t_{D}} = \sqrt{\frac{1 + \left( \frac{K^{2}}{R^{2}} \right)_{S}}{1 + \left( \frac{K^{2}}{R^{2}} \right)_{D}}}$
$= \sqrt{\frac{1 + \frac{2}{5}}{1 + \frac{1}{2}}} = \sqrt{\frac{14}{15}}$

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.