Worked Example

Problem:
A block of mass $2 \, \text{kg}$ is on a rough surface with $\mu_k = 0.2$. Find friction force.

Solution

Normal force:

$$ N = mg = 2 \times 9.8 = 19.6 $$

Friction:

$$ f_k = \mu_k N = 0.2 \times 19.6 = 3.92 \, \text{N} $$