In the arrangement shown in the figure,the coefficient of friction between the two blocks is $0.5$. The force of friction between the two blocks is (Assume that the $4 \,kg$ block is placed on a smooth horizontal surface.) (Acceleration due to gravity $= 10 \,ms^{-2}$.) (in $\,N$)

Two blocks $A$ and $B$ of masses $4 \ kg$ and $6 \ kg$ are as shown in the figure. $A$ horizontal force of $12 \ N$ is required to make $A$ slip over $B$. Find the maximum horizontal force $F_B$ that can be applied on $B$ so that both $A$ and $B$ move together. (Take $g=10 \ m \ s^{-2}$) (in $N$)

Two blocks of masses $M$ and $m$ are placed on one another on a smooth horizontal surface as shown in the figure. The force $F$ is acting on the mass $M$ horizontally during time interval $t$. Assuming no relative sliding between the blocks,the work done by friction on the blocks is .......... .

$A$ pen of mass $m$ is lying on a piece of paper of mass $M$ placed on a rough table. If the coefficients of friction between the pen and paper and the paper and the table are $\mu_1$ and $\mu_2$,respectively,then the minimum horizontal force with which the paper has to be pulled for the pen to start slipping is given by:

Find the maximum force $F$ (in $N$) which will not cause motion of any of the blocks as shown in the figure.

$A$ truck of mass $8 \text{ ton}$ is carrying a block of mass $2 \text{ ton}$. If a breaking force of $25 \text{ kN}$ is applied on the truck, then the frictional force acting on the block is (Coefficient of static friction between the block and the truck is $0.3$) (in $\text{ N}$)