In which of the following cases is the contact force between $A$ and $B$ maximum $(m_A = m_B = 1 kg)$

Two blocks $A$ and $B$ of masses $3\,m$ and $m$ respectively are connected by a massless and inextensible string. The whole system is suspended by a massless spring as shown in figure. The magnitudes of acceleration of $A$ and $B$ immediately after the string is cut, are respectively

A block of mass $m$ is placed on a smooth inclined wedge $ABC$ of  inclination $\theta$ as shown in the figure. The wedge is given an acceleration $a$ towards the right. The relation between $a$ and $\theta$ for the block to remain stationary on the wedge is

A block of mass $8\, kg$ is at rest on a rough inclined plane as shown in figure. The magnitude of net force exerted by the surface on the block will be ......... $N$

In the diagram shown, the normal reaction force between $2\,kg$ and $1\,kg$ is (Consider the surface, to be smooth)$.........N$ (Given $g =10\,ms ^{-2}$)

A block of mass $M$ is pulled along a horizontal frictionless surface by a rope of mass $m$. If a force $P$ is applied at the free end of the rope, the force exerted by the rope on the block will be