10-3 A helical compression spring is wound using 2.5-mm-diameter music wire. The spring has an outside diameter of 31 mm with plain ground ends, and 14 total coils. (a) Estimate the spring rate. (b) What force is needed to compress this spring to closure? (c) What should the free length be to ensure that when the spring is compressed solid the torsional stress does not exceed the yield strength? (d) Is there a possibility that the spring might buckle in service?