[tex]\text{Scriem principiul al doilea al mecanicii pentru corp:}\\\overrightarrow{F}+\overrightarrow{N}+\overrightarrow{G}+\overrightarrow{F_f}=m\overrightarrow{a}\hspace{10pt}(1)\\\\\text{Proiectam $(1)$ pe axa Oy: }N-G=0\implies N=G=mg\hspace{10pt}(2)\\\text{Proiectam $(1)$ pe axa Ox: }F-F_f=ma\hspace{10pt}(3)\\\text{Dar, }F_f=\mu N \overset{(2)}{\implies} F_f=\mu mg \overset{(3)}{\implies} F-\mu mg=ma \implies\\F=m(a+\mu g)\\[/tex][tex]\text{a) Corpul se misca cu viteza constanta }\iff a=0\quad(\overrightarrow{a}=\overrightarrow{0})\\\implies F=\mu mg=6,17\:N\\\\\text{b)} \:F=m(a+\mu g)=9,17\:N[/tex]
