Q. A reel of thread unrolls itself falling down under gravity. Neglecting mass of the thread, the acceleration of the reel is
A) $g$
B) $g/2$
C) $2g/3$
D) $4g/3$
Explanation
(c) $a = \frac{g}{1 + \frac{K^{2}}{R^{2}}}$ [For solid cylinder $\frac{K^{2}}{R^{2}} = \frac{1}{2}$]
$\therefore a = \frac{g}{1 + \frac{1}{2}} = \frac{2}{3}g$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.