솔루션피아

$$\begin{cases} m_A&=10\ut{kg}\\m_B&=5.0\ut{kg}\\\theta&=30\degree\end{cases}$$$$0=\vec F_A+\vec F_B+\vec T,$$$$\begin{aligned}\tan\theta&={F_A\over F_B}\\&={\mu m_Ag\over m_Bg}\\\end{aligned}$$$$\begin{aligned}\mu&={m_B\over m_A}\tan\theta\\&={1\over2\sqrt3}\\&\approx 0.2886751345948129\\&\approx 0.29\\\end{aligned}$$

$$\begin{cases} M&=m_b+m_p=89.00\ut{kg}\\T_a&=500\ut{N}\\T_b&=700\ut{N}\\g&=9.80665\ut{m/s^2}\end{cases}$$$$\put {x\over L}=k,$$$$\Sigma \tau=0,$$$$\begin{aligned}0&=-{L\over2}m_bg-\br{x\over L}Lm_pg+LT_y \\&={m_bg}+2km_pg-2T\sin\theta \\\end{aligned}$$$$\begin{cases} 0&={m_bg}+2\br{0}m_pg-2\br{500}\sin\theta \\0&={m_bg}+2\br{1}m_pg-2\br{700}\sin\theta \\89&=m_b+m_p\end{cases}$$$$\ab{a,b,..