$A$ block of mass $4 \text{ kg}$ is placed on a horizontal surface having coefficients of static and kinetic friction as $0.5$ and $0.4$ respectively. If a force of $4 \text{ N}$ is applied parallel to the horizontal surface, then the force of friction acting on the body will be $\left[g = 10 \text{ m/s}^2\right]$ (in $\text{ N}$)

$A$ block of mass $M$ is held against a rough vertical wall by pressing it with a finger. If the coefficient of friction between the block and the wall is $\mu$ and the acceleration due to gravity is $g$,calculate the minimum force required to be applied by the finger to hold the block against the wall.

What is the maximum acceleration of a train such that a $50 \ kg$ box lying on its floor remains stationary (in $m \ s^{-2}$)? (Given: Coefficient of static friction between the box and the train's floor is $0.3$ and $g = 10 \ m \ s^{-2}$)

Given below are two statements:
$Statement$ $(I)$: The limiting force of static friction depends on the area of contact and is independent of materials.
$Statement$ $(II)$: The limiting force of kinetic friction is independent of the area of contact and depends on materials.
In the light of the above statements,choose the most appropriate answer from the options given below:

$A$ body of mass $2 \,kg$ is on an inclined plane of inclination $30^{\circ}$ and the coefficient of friction is $\frac{1}{\sqrt{3}}$. The minimum force required to move the body up the inclined plane is (Acceleration due to gravity $g = 10 \,ms^{-2}$) (in $\,N$)

$A$ block of mass $M$ is placed on a horizontal surface and it is tied with an inextensible string to a block of mass $m$,as shown in the figure. $A$ block of mass $m_0$ is also placed on $M$. If $\mu$ is the coefficient of friction between the block $M$ and the horizontal surface,then the minimum value of $m_0$ required to keep the block $m$ stationary is