5-12 할리데이 11판 솔루션 일반물리학

$$ \begin{cases} m_A&=4.00\ut{kg}\\ m_B&=9.00\ut{kg}\\ m_C&=12.0\ut{kg}\\ g&=9.80665\ut{m/s^2} \end{cases} $$ $$\Sigma \vec F = m\vec a,$$ $$ \begin{cases} \Sigma \vec F_A &= m_A\vec a\\ \Sigma \vec F_B &= m_B\vec a\\ \Sigma \vec F_C &= m_C\vec a\\ \end{cases} $$ $$ \begin{cases} T_{AB}-m_Ag &= m_A a\\ T_{BC}-T_{AB} &= m_B a\\ m_Cg-T_{BC} &= m_C a\\ \end{cases} $$ $$ \begin{aligned} T_{BC}&=\frac{204g}{25}\\ &\approx 80.02226399999999\ut{N}\\ &\approx 80.0\ut{N}\\ \end{aligned} $$