Question

A block of mass 5kg rests on a rough horizontal surface. It is found that a force of 10 N is required to make the block just move. However, once the motion begins, a force of only 8N is enough to maintain the motion. Find the coefficients of kinetic and static friction between the block and the horizontal surface.

Answer 1

Just move,

$\to$ static friction will apply

$f_s=10N={\mu }_{3}N$

$\Rightarrow {\mu }_s=\frac{10}{50}=0.2$

After start of motion

kinetic friction will apply

$f_k=8N={\mu }_{k}N$

${\mu }_k=\frac{8}{50}=0.175$