The uniform rectangular door panel has a mass of 25 kg and is held in equilibrium above the horizontal at the position θ = 60° by rod BC. Determine the required stiffness of the torsional spring at A, so that the door's angular velocity becomes zero when the door reaches the closed position (θ = 0°) once the supporting rod BC is removed. The spring is undeformed when θ = 60°.

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1.2 m 0 = 60° ΑΙ B