A door is closed under the control of a spring and dashpot. Thespring gives a torque of 13.5 Nm when the door is closed and has astiffness of 50 N.m/rad. The dashpot gives a damping torque of 100N.m.s/rad. The moment of inertia of the door about its hinges is 90Kg.m2. Derive an expression for the motion of the door if it isopened 90o and released and find approximately the time it takes toclose
