A box of mass 120 g was resting on a smooth horizontal table that had a smooth pulley fixed at each end. A light inextensible string is connected to the box and is passed over one of the pulleys, . The other end of the string is attached to body , of mass 470 g, which was hanging freely vertically below the . Another similar string is connected to the other side of the box and is passed over the other pulley, , and connected to body , of mass 390 g, which was hanging freely vertically below . When the box was 260 cm away from pulley , the system was released from rest. One second later, the mass of body was reduced by 80 g. Find the time, , taken from the moment the weight of body was reduced until the box collides with pulley . Take .