When θ= 0 ̊, the assembly is held at rest, and the torsional spring is untwisted. if the assembly is released and falls downward, determine its angular velocity at the instant θ= 90 ̊. rod ab has a mass of 6 kg, and the disk c has a mass of 9 kg. note: the moment due to a torsional spring is, m = kθ; where k is the stiffness of the spring?