Two masses $A$ and $B$ are connected by a spring.$A$ has mass $M$,$B$ a mass $2M$, and the spring has a negligible mass. The spring is compressed so that the potential energy stored in it is $V_0$ . The system is placed on a horizontal frictionless table and is given a velocity $u\hat{k}$ in the $z-$direction as shown, and the spring is released. In the subsequent motion the line from $B$ to $A$ always points along the$\hat{i}$ unit vector. The initial total mechanical Energy