The collar having mass mc = 2 kg, slides without friction along the shaft. Attached to the collar is a spring of stiffness k. The system starts in position 1 and is given an initial speed down the shaft of v1 = 1 m/s. The collar then momentarily comes to rest at position 2, when the spring is horizontal. If L1 = 2L2 , and the unstretched length of the spring is L1 = 0 = 1 m, determine the spring stiffness, k. Assume = 30° and gravity acts in the downward vertical direction.