Two masses 4 kg and 6 kg are attached to the ends of an inextensible string over a pulley. The weights of the string and pulley are much smaller than the two masses attached and so are neglected. The pulley is also assumed to be smooth so that the tension T' is the same on both sides of the pulley. The masses are held at the same level and the system is released from rest. What is the speed of the 6 kg mass when it has fallen 2 metres?