Two masses m1 and m2 are connected by a massless spring of constant k and unstretched length L. The masses are placed on a frictionless straight channel, which is considered as x -axis. They are initially at rest at x=0 and x=L respectively. At t=0, a velocity of v0 is suddenly imparted to the first particle. At a later time t0, the centre of mass of the two masses is at x=