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

$A$ $20\, kg$ block is initially at rest on a rough horizontal surface. $A$ horizontal force of $75\, N$ is required to set the block in motion. After it is in motion,a horizontal force of $60\, N$ is required to keep the block moving with constant speed. The coefficient of static friction is

For a given mass,how does rolling friction compare to static friction and kinetic friction?

$A$ 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.

The maximum force of friction is called:

$A$ person initially at rest starts walking towards the east without slipping or skidding. What is the type of friction acting on the person from the ground, and in which direction does the frictional force act?