6-62 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} \theta&=40.0\degree\\ \mu_k&=0.0400\\ m&=85.0\ut{kg}\\ A&=1.25\ut{m^2}\\ C&=0.140\\ \rho&=1.20\ut{kg/m^2}\\ \end{cases} $$ $$\Sigma \vec F = 0 \Harr \Delta \vec v=0,$$ $$ \begin{cases} \Sigma F_x &= 0\\ \Sigma F_y &= 0\\ \end{cases} $$ $$D=\frac{1}{2}C\rho Av^2,$$ $$ \begin{cases} 0 &= mg\sin\theta-\mu N-\frac{1}{2}C\rho Av^2\\ 0 &= N-mg\cos\theta\\ \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} v_a&=\sqrt{\frac{2mg (\sin\theta-\mu\cos\theta)}{C\rho A}}\\ &\approx 69.71120654977588\ut{m/s}\\ &\approx 69.7\ut{m/s}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} v_b&=\sqrt{\frac{2mg (\sin\theta-\mu\cos\theta)}{(dC)\rho A}}\\ &=\frac{v_a}{\sqrt{d}}\\ \end{aligned} $$