A helical compression spring with squared and ground ends is required to exert a maximum working force of 1000 N, and a force of 500 N when the spring is 60 mm longer. Sufficiently few load cycles will be involved to justify designing the spring on the basis of static loading. An existing supply of 5-mm diameter music wire will be used. The spring is to be preset . Determine appropriate values for D, N, and Lf. Check for possible buckling.