Correct option: (D) [(2mg) / (M + 2m)]
Explanation:
When a point mass is connect string which is wound round solid body.
then when mass is released,
acceleration of point mass = a = [g / {1 + (I / mR2)}]
here I = [(MR2) / α]–– for solid cylinder,
hence
a = [g / {1 + {{(MR2) / 2} / (mR2)}}]
= [g / {1 + {1 / (2m)}}]
= [(2mg) / (M + 2m)]