6-36 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} N&=20\\ m&=5.0\times10^4\ut{kg}\\ f&=250v\\ v_1&=30\ut{km/h}=\frac{25}{3}\ut{m/s}\\ a_1&=0.20\ut{m/s^2} \end{cases} $$ $$\ab{a}$$ $$\Sigma \vec F = m\vec a,$$ $$F_T-Nf=Nm a $$ $$ \begin{aligned} F_T&=Nma+Nf\\ &=\frac{725000}{3}\ut{N}\\ &\approx 241666.66666666666\ut{N}\\ &\approx 2.4\times10^5\ut{N}\\ &\approx 0.24\ut{MN}\\ \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} \Sigma F&=0\\ \end{aligned} $$ $$ \begin{aligned} 0&=F_T-Nf-Nmg\sin\theta\\ &=Nma+Nf-Nf-Nmg\sin\theta\\ &=a-g\sin\theta\\ \end{aligned} $$ $$ \begin{aligned} \theta&=\sin^{-1}\frac{a}{g}\\ &=\sin^{-1}\frac{1}{5g}\\ &\approx 0.020395738287555556\ut{rad}\\ &\approx 0.02\ut{rad}\\ \end{aligned} $$