When a constant force is applied to a body, it moves with uniform

For 1kg mass v-t graph is as shown, then which of the following is true?

Two forces of $6 \text{N}$ and $3\text{ N}$ are acting on two blocks of $2 \text{kg}$ and $1\text{ kg}$ kept on frictionless floor. What is the force exerted on $2\text{ kg}$ block by $1 \text{kg}$ block?

Three masses of $1 \text{kg}, 6 \text{kg} and 3 \text{kg}$ are connected to each other with threads and are placed on the table as shown in figure. What is the acceleration with which the system is moving?

Take $g=10 \raisebox{1ex}{$\text{m}$}\!\left/ \!\raisebox{-1ex}{${\text{s}}^2$}\right.$.

Two blocks of mass $4 \text{kg}$ and $2\text{ kg}$ are connected by a heavy string and placed on rough horizontal plane. The $2 \text{kg}$ block is pulled with a constant force $F$. The coefficient of friction between the blocks and the ground is $0.5$. What is the value of $F$ so that tension in the string is constant throughout during motion of the blocks. $\left(g=10 \raisebox{1ex}{$\text{m}$}\!\left/ \!\raisebox{-1ex}{${\text{s}}^2$}\right.\right)$

A string of negligible mass going over a clamped pulley of mass $m$ supports a block of mass $M$ as shown in the figure. The force on the pulley by the clamp is given by