Determine the stiffness k of the torsional spring at A, so that if the bars are released f...

Determine the stiffness k of the torsional spring at A, so that if the bars are released from rest when θ = 0°, bar AB has an angular velocity of 0.5 rad/s at the closed position, θ = 90°. The spring is uncoiled when θ = 0°. The bars have a mass per unit length of 10 kg/m.