11-49 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} \tau_0&=8.0\ut{N\cdot m}\\ \omega_0&=0\\ \end{cases} $$ $$\vec \tau_\net=\dyt{\vec L},$$ $$ \begin{aligned} L&=L_0+\Delta L\\ &=0+\int_0^t \tau \dd t\\ &=\int_0^t \tau \dd t\\ \end{aligned} $$ $$\ab{a}$$ $$ \begin{aligned} L_7 &=\int_0^7 \tau \dd t\\ &=7\cdot6+{1\over2}\cdot \br{2+4}\cdot 2\\ &=48\ut{kg\cdot m^2/s} \end{aligned} $$ $$\ab{b}$$ $$ \begin{aligned} L_{20} &=\int_0^{20} \tau \dd t\\ &={1\over2}\cdot \br{2+4}\cdot 2+{1\over2}\cdot \br{7+9}\cdot 6-{1\over2}\cdot \br{11+6}\cdot 6\\ &=3\ut{kg\cdot m^2/s} \end{aligned} $$