Answer
$v = \sqrt{\frac{mgR}{M}}$
Work Step by Step
The tension in the cord $F_T$ provides the force to keep the puck moving in a circle. Therefore: $F_T = M\frac{v^2}{R}$
Since the tension in the cord holds up the dangling block, the tension in the cord must be equal to the weight of the dangling mass. Therefore: $F_T = mg$
$M\frac{v^2}{R} = mg$
$v = \sqrt{\frac{mgR}{M}}$
