6-30 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} v&=70\ut{km/h}=\frac{175}{9}\ut{m/s}\\ R&=170\ut{m}\\ g&=9.80665\ut{m/s^2} \end{cases} $$ $$\ab{a}$$ $$ \begin{cases} \Sigma F_R&=\cfrac{mv^2}{R}\\ \Sigma F_y&=0 \end{cases} $$ $$ \begin{cases} \cfrac{mv^2}{R}&=F_N\sin\theta\\ 0&=F_N\cos\theta-mg \end{cases} $$ $$ \begin{aligned} \theta&=\tan^{-1}\frac{v^2}{gR}\\ &\approx 0.22301633395178838\ut{rad}\\ &\approx 0.22\ut{rad}\\ \end{aligned} $$ $$\ab{b}$$ $$\Sigma F_R=\frac{mv^2}{R}=\mu mg$$ $$ \begin{aligned} \mu &=\frac{v^2}{gR}\\ &=\frac{6125}{2754g}\\ &\approx 0.22678873654647097\\ &\approx 0.23\\ \end{aligned} $$