$A$ string is wrapped around a cylinder of radius $r$ and moment of inertia $I$. $A$ mass $m$ is attached to one end of the string. The cylinder can rotate freely about its horizontal axis. If the mass $m$ is released from rest at a height $h$,what will be its velocity?

• A
  $(2gh)^{1/2}$
• B
  ${\left( {\frac{{2mgh{r^2}}}{I}} \right)^{1/2}}$
• C
  ${\left( {\frac{{2mgh{r^2}}}{{I + m{r^2}}}} \right)^{1/2}}$
• D
  ${\left( {\frac{{mgh{r^2}}}{{I + 2m{r^2}}}} \right)^{1/2}}$