The tension in the string connected between blocks is ......... $N$

Three blocks $A, B$ and $C,$ of masses $4\, kg, \,2 \,kg$ and $1\, kg$ respectively, are in contact on a frictionless surface, as shown. If a force of $14\, N$ is applied on the $4 \,kg$ block, then the contact force between $A$ and $B$ is  .......... $N$

Three identical blocks of masses $m=2\; k g$ are drawn by a force $F=10.2\; N$ with an acceleration of $0.6\; ms ^{-2}$ on a frictionless surface, then what is the tension (in $N$) in the string between the blocks $B$ and $C$?

Two particle of mass $m$ each are tied at the ends of a light string of length $2 \mathrm{a}$. The whole system is kept on a frictionless horizontal surface with the string held tight so that each mass is at a distance $'a'$ from the center $\mathrm{P}$ (as shown in the figure). Now, the mid-point of the string is pulled vertically upwards with a small but constant force $F$. As a result, the particles move towards each other on the surface. The magnitude of acceleration, when the separation between them becomes $2 \mathrm{x}$ is

A uniform rope of mass $1.0\, kg$ is connected with a box of mass $2.0\, kg$, which is placed on a smooth horizontal surface. The free end of the rope is pulled horizontally by a force $6\, N$. Find the tension at the midpoint of the rope ....... $N$