A block of mass $m=5\text{ kg}$ is resting on a horizontal surface. If the coefficient of static friction is ${\mu }_s=0.2$, what is the maximum static frictional force $f_{s,max}$ in Newtons? (Take $g=10{\text{ m/s}}^2$)

Solution

1. The normal force $N$ on a horizontal surface is $N=mg$.
2. Calculate the normal force: $$\begin{array}{rl}N& =5\times 10\\ & =50\text{ N}\end{array}$$.
3. The maximum static friction is $f_{s,max}={\mu }_{s}N$.
4. Calculate the value: $$\begin{array}{rl}{f}_{s,max}& =0.2\times 50\\ & =10\text{ N}\end{array}$$.
5. Hence the answer is (C).