Three masses of $16 \, kg$,$8 \, kg$,and $4 \, kg$ are placed in contact as shown in the figure. If a force of $140 \, N$ is applied on the $4 \, kg$ mass,then the force on the $16 \, kg$ mass will be ............ $N$.

Two blocks $A$ and $B$,each of mass $m$,are placed on a smooth horizontal surface. Two horizontal forces $F$ and $2F$ are applied on the two blocks $A$ and $B$ respectively,as shown in the figure. The block $A$ does not slide on block $B$. Then,the normal reaction acting between the two blocks is

$A$ force $F = 10t$ acts on a block of mass $10 \, kg$ as shown in the figure. Find the time $t$ when the block loses contact with the surface.

Two rectangular blocks of masses $40 \ kg$ and $60 \ kg$ are connected by a string and kept on a frictionless horizontal table. If a force of $1000 \ N$ is applied on the $60 \ kg$ block away from the $40 \ kg$ block,then the tension in the string is: (in $N$)

If the breaking strength of a rope is $\frac{4}{3}$ times the weight of a person,then the maximum acceleration with which the person can safely climb up the rope is ($g$ = acceleration due to gravity).

The maximum tension a rope can withstand is $60 \,kg$-wt. The ratio of maximum acceleration with which two boys of masses $20 \,kg$ and $30 \,kg$ can climb up the rope at the same time is