The bar has a weight of 6 lb. If the stiffness of the spring is k = 8 lb/ft and the dash...

The bar has a weight of 6 lb. If the stiffness of the spring is k = 8 lb/ft and the dashpot has a damping coefficient c = 60 lb s/ft, determine the differential equation which describes the motion in terms of the angle θ of the bar's rotation. Also, what should be the damping coefficient of the dashpot if the bar is to be critically damped?