Q. A uniform disc of mass $M$ and radius $R\ $is mounted on a fixed horizontal axis. A block of mass $m$ hangs from a massless string that is wrapped around the rim of the disc. The magnitude of the acceleration of the falling block ($m$) is
A) $\frac{2M}{M + 2m}\ g$
B) $\frac{2m}{M + 2m}\ g$
C) $\frac{M + 2m}{2\ M\ }\ g$
D) $\frac{2M + m}{2M\ }\ g$
Explanation
(b) When pulley has a finite mass $M$ and radius $R$,
then tension in two segments of string are
different.
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Here, $ma = mg - T$
$a = \frac{m}{m + \frac{M}{2}}g = \frac{2m}{2m + M}g$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.