What will be the acceleration of the system and tension in the rope connecting $5\,kg$ and $1\,kg$ blocks?

Two blocks $A$ and $B$ of mass $m$ and $2m$ respectively are connected by a massless spring of force constant $k$. They are placed on a smooth horizontal plane. The spring is stretched by an amount $x$ and then released. The relative velocity of the blocks when the spring comes to its natural length is:

For the given figure,what will be the contact force applied by the $6 \ kg$ block on the $4 \ kg$ block? ............ $N$

$A$ rope of mass $5 \,kg$ is moving vertically in a vertical position with an upward force of $100 \,N$ acting at the upper end and a downward force of $70 \,N$ acting at the lower end. The tension at the midpoint of the rope is ......... $N$.

Two masses $A$ and $B$,each of mass $M$,are connected by a massless spring. $A$ force $F$ acts on the mass $B$ as shown in the figure. If the mass $A$ starts moving away from mass $B$ with acceleration $a$,then the acceleration of mass $B$ will be:

Two objects $A$ and $B$,each of mass $m$,are connected by a light inextensible string. They are restricted to move on a frictionless ring of radius $R$ in a vertical plane (as shown in the figure). The objects are released from rest at the position shown. Then,the tension in the cord just after release is