Theo định luật II Newton:
$\vec{P}+ \vec{N}+ \vec{F}+ \vec{F_{ms}}= \vec{0}$ (*)
(*) $\buildrel{{Ox}}\over\longrightarrow Fcos\alpha = F_{ms}$
$\Leftrightarrow Fcos\alpha= \mu.N$ (1)
(*) $\buildrel{{Oy}}\over\longrightarrow -P+ N + Fsin\alpha= 0$
$\Leftrightarrow N= P - Fsin\alpha= mg - Fsin\alpha$ (2)
(1)(2) => $\mu= \frac{Fcos\alpha}{mg-Fsin\alpha}= 0,12$