6-40 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} m&=6.70\ut{kg}\\ \mu&=0.850\\ \theta&=65.0\degree\\ g&=9.80665\ut{m/s^2} \end{cases} $$ $$\Sigma \vec F = 0 \Harr \Delta \vec v=0,$$ $$ \begin{cases} \Sigma F_x &= 0\\ \Sigma F_y &= 0\\ \end{cases} $$ $$ \begin{cases} 0 &= F\cos\theta-\mu N\\ 0 &= F\sin\theta-mg-N\\ \end{cases} $$ $$0 = F\cos\theta-\mu (F\sin\theta-mg)$$ $$ \begin{aligned} F&=\frac{\mu mg}{\mu\sin\theta-\cos\theta}\\ &\approx 160.60370554075706\ut{N}\\ &\approx 161\ut{N}\\ \end{aligned} $$