$16\mathrm{.}88$ Two identical $17\mathrm{.}8-N$ slender rods $AB$ and $BC$ are connected by a pin at $B$ and by the cord $AC.$ The assembly rotates in a vertical plane under the combined effect of gravity and an $8-N*m$ couple $M$ applied to rod $AB.$ Knowing that in the position shown the angular velocity of the assembly is zero, determine $($a$)$ the angular acceleration of the assembly, $($b$)$ the tension in cord $AC.$