5-36 할리데이 11판 솔루션 일반물리학

$$\begin{cases} m&=120\ut{kg}\\ \theta&=35.0\degree\\ \end{cases}$$ $$\Sigma \vec F = 0 \Harr \Delta \vec v=0,$$ $$\begin{cases} \Sigma F_x &= 0\\ \Sigma F_y &= 0\\ \end{cases}$$ $$\begin{cases} F\cos\theta-mg\sin\theta &= 0\\ F_N-F\sin\theta -mg\cos\theta&= 0\\ \end{cases}$$ $$\ab{a}$$ $$\begin{aligned} F&=\frac{mg\sin\theta}{\cos\theta}\\ &=mg\tan\theta\\ &=120g\tan35\degree\\ &\approx 824.0028305501099\ut{N}\\ &\approx 824\ut{N}\\ \end{aligned}$$ $$\ab{b}$$ $$\begin{aligned} F_N &= F\sin\theta+mg\cos\theta\\ &= mg\tan\theta\sin\theta+mg\cos\theta\\ &= \frac{mg}{\cos\theta}\\ &= \frac{120g}{\cos35\degree}\\ &\approx 1436.605094505304\ut{N}\\ &\approx 1.44\times 10^3\ut{N}\\ &\approx 1.44\ut{kN}\\ \end{aligned}$$