$A$ system consists of three masses $m_1$,$m_2$,and $m_3$ connected by a string passing over a pulley $P$. The mass $m_1$ hangs freely,and $m_2$ and $m_3$ are on a rough horizontal table (the coefficient of friction $= \mu$). The pulley is frictionless and of negligible mass. Find the downward acceleration of mass $m_1$. (Assume $m_1 = m_2 = m_3 = m$)

• A
  $\frac{g(1 - g\mu)}{9}$
• B
  $\frac{2g\mu}{3}$
• C
  $\frac{g(1 - 2\mu)}{3}$
• D
  $\frac{g(1 - 2\mu)}{2}$