Two blocks $$A$$ and $$B$$, of masses $$M$$ and $$2M$$, respectively, are connected by a massless spring of natural length $$L_0$$ and spring constant $$K$$. The blocks are initially at rest on a smooth horizontal floor with spring at its natural length $$L_0$$. A third block $$C$$ of mass $$M$$, identical to that of block $$A$$, moves on the floor with speed $$v$$ along the line joining $$A$$ and $$B$$ and collides with $$A$$ elastically. In the subsequent motion