The limiting friction is

$A$ block of mass $2 \, kg$ is kept on the floor. The coefficient of static friction is $0.4$. If a force $F$ of $2.5 \, N$ is applied on the block as shown in the figure,the frictional force between the block and the floor will be ........ $N$.

$A$ 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.

$A$ block of weight $W$ is held against a vertical wall by applying a horizontal force $F$. The minimum value of $F$ needed to hold the block is $[\mu < 1]$.

Calculate the maximum acceleration (in $m s^{-2}$) of a moving car so that a body lying on the floor of the car remains stationary. The coefficient of static friction between the body and the floor is $0.15$ $(g = 10 m s^{-2})$.

In the figure shown,a horizontal force $F_1$ is applied on a block,but the block does not slide. Then,as the magnitude of the vertical force $F_2$ is increased from zero,the block begins to slide. Which of the following statements is correct?