Question

A body of mass $5kg$ is placed on a rough horizontal surface. If coefficients of static and kinetic friction are $0.5$ and $0.4$ respectively, then find the value of force of friction when external applied horizontal external force is (i) $15N$ (ii) $25N$ and (iii) $35N$

Answer 1

Here , maximum value of static friction that can act on the body = ${\mu }_{s}mg$

= $25$ N

(i) Since the applied force is less than the maximum possible value of static friction

therefore , the force of friction will be just enough to stop the motion of the body.

Here , friction force = $15$ N

(ii) Here, applied force = maximum possible value of static friction.

Friction force = $25$ N

(iii) Here , applied force > maximum value of static friction.

Therefore , the body moves and kinetic friction acts on the body.

Friction force = ${\mu }_{k}mg$ = $20$ N.