$A$ block of mass $m$ is kept on a platform which starts from rest with constant acceleration $g/2$ upward,as shown in the figure. Work done by the normal reaction on the block in time $t$ is

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

Three blocks of masses $m$,$2m$,and $3m$ are pushed with a force $F$ across a frictionless table as shown in the figure. Let $N_{1}$ be the contact force between the left two blocks ($m$ and $2m$) and $N_{2}$ be the contact force between the right two blocks ($2m$ and $3m$). Then:

$A$ lift of mass $m$ is ascending with an acceleration $a$ $(a < g)$. The tension in the cable of the lift is $(g = \text{acceleration due to gravity})$

$A$ man slides down a light rope whose breaking strength is $\eta$ times the weight of the man $(\eta < 1)$. What is the maximum acceleration of the man so that the rope does not break?

$A$ body of mass $8\,kg$ is hanging from another body of mass $12\,kg$. The combination is being pulled upwards by a string with an acceleration of $2.2\,m/s^2$. The tensions $T_1$ (in the top string) and $T_2$ (in the string between the two masses) will be respectively: (use $g = 9.8\,m/s^2$)