The maximum value of static friction is called:

What is friction? Explain static frictional force.

$A$ body of mass $m$ is kept on a rough horizontal surface (coefficient of friction $= \mu$). $A$ horizontal force is applied on the body,but it does not move. The resultant of the normal reaction and the frictional force acting on the object is given by $F$,where $F$ is:

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:

$A$ block of mass $m$ is pressed against a vertical surface by a spring of unstretched length $l$. The spring is compressed by a distance $d$ as shown in the figure. If the coefficient of friction between the block and the surface is $\mu$,choose the correct statement.

Find the minimum value of mass $m$ that should be placed on the $20 \, kg$ block so that the system remains at rest. (Given coefficient of friction $\mu = 0.25$) (in $, kg$)