For the given system,what is the contact force (in $N$) acting on the $4 \, kg$ block?

For the given arrangement of blocks on a frictionless surface,the tension $T_2$ is:

$A$ block of mass $m_1$ rests on a horizontal table. $A$ string tied to the block is passed over a frictionless pulley fixed at the end of the table,and to the other end of the string is hung another block of mass $m_2$. The acceleration of the system 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.

$A$ monkey of mass $40 \, kg$ climbs on a rope which can stand a maximum tension of $600 \, N$. In which of the following cases will the rope break: the monkey
$(a)$ climbs up with an acceleration of $6 \, m \, s^{-2}$
$(b)$ climbs down with an acceleration of $4 \, m \, s^{-2}$
$(c)$ climbs up with a uniform speed of $5 \, m \, s^{-1}$
$(d)$ falls down the rope nearly freely under gravity? (Ignore the mass of the rope).

$A$ block of mass $m$ slides down on a wedge of mass $M$ as shown in the figure. Let $\vec a_1$ be the acceleration of the wedge and $\vec a_2$ be the acceleration of the block with respect to the ground. $N_1$ is the normal reaction between the block and the wedge,and $N_2$ is the normal reaction between the wedge and the ground. Friction is absent everywhere. Select the incorrect alternative.