What force should be applied on the wedge so that block over it does not move? (All surfaces are smooth)

Two wooden blocks are moving on a smooth horizontal surface such that the mass $m$ remains stationary with respect to block of mass $M$ as shown in the figure. The magnitude of force $P$ is

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

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

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. ............ $N$

A mass $M$ is placed on a very smooth wedge resting on a surface without friction. Once the mass is released, the acceleration to be given to the wedge so that $M$ remains at rest is $a$ where