10-25 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} 2R&=8.0\ut{cm}\\ R&=4.0\times10^{-2}\ut{m}\\ L&=8.2\ut{m}\\ \omega_0&=0\\ \alpha&=0.86\ut{rad/s^2}\\ \end{cases} $$ $$\ab{a}$$ $$ \begin{aligned} \theta&=\frac{L}{r},\\ &=205\ut{rad}\\ &\approx 2.1\times10^2\ut{rad}\\ \end{aligned} $$ $$\ab{b}$$ $$\Delta \theta=\omega_0t+\frac{1}{2}\alpha t^2,$$ $$ \begin{aligned} t&=\sqrt\frac{2\Delta \theta}{\alpha}\\ &=10\sqrt\frac{205}{43}\ut{s}\\ &\approx 21.83447242427697\ut{s}\\ &\approx 22\ut{s}\\ \end{aligned} $$