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 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 ____________ m/s. (Assume string does not slip and \(g=10\,\text{m s}^{-2}\)).