Two identical blocks with mass m, connected by a light spring (neither compressed nor stretched), slide with speed v0 on a frictionless surface towards a wall (see gure below).
At t = 0 the left block is at distance L from the wall. Find the time after which the center of mass of this system will be again at the position it was when t = 0.
Assume that the block collides with the wall elastically, and the duration of the collision is negligibly short. The force constant of the spring is k.
