A mass m hangs with the help of a string wrapped around a pulley on a frictionless bearing. The pulley has mass m and radius R. Assuming pulley to be a perfect uniform circular disc, the acceleration of the mass m, if the string does not slip on the pulley, is

Question

( A ) $\frac{g}{3}$
( B ) $g$
( C ) $\frac{3}{2} g$
( D ) $\frac{2}{3} g$