Static friction between two surfaces:

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?

$A$ heavy body of mass $25 \ kg$ is to be dragged along a horizontal plane $\left( \mu = \frac{1}{\sqrt{3}} \right)$. The least force required is ........ $kgf$.

$A$ 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 $[\mu < 1]$.

$A$ body of mass $10 \ kg$ slides along a rough horizontal surface. The coefficient of friction is $1/\sqrt{3}$. Taking $g = 10 \ m/s^2$,the least force which acts at an angle of $30^\circ$ to the horizontal is ...... $N$.

In the figure shown,a block of weight $10 \, N$ is resting on a horizontal surface. The coefficient of static friction between the block and the surface is ${\mu _s} = 0.4$. $A$ force of $3.5 \, N$ will keep the block in uniform motion,once it has been set in motion. If a horizontal force of $3 \, N$ is applied to the block,then the block will: