A door AB weighing 80 lb is pinned at A and swings in the horizontal plane. The spring CD...

A door AB weighing 80 lb is pinned at A and swings in the horizontal plane. The spring CD has stiffness k and is unstretched when θ = 0°. Let L = 1.5 ft and h = 0.5 ft.

If the door is rotating counterclockwise and the speed of B is 10 ft/s when θ = 0, determine k, such that the door temporarily stops when θ = 90°. Assume that the spring does not impinge on the mount at A.

Figure P8.16