Two masses \( m \) and \( 2m \) are connected by a light string going over a pulley (disc) of mass \( 30m \) with radius \( r = 0.1 \, \text{m} \). The pulley is mounted in a vertical plane and it is free to rotate about its axis. The \( 2m \) mass is released from rest and its speed when it has descended through a height of \( 3.6 \, \text{m} \) is ______ \( \text{m/s} \). (Assume string does not slip and \( g = 10 \, \text{m/s}^{2} \))