A close-coiled helical spring has 60 coils and is made of wire that is 6 mm in diameter. The mean coil diameter is 85 mm. Determine the maximum shear stress in the wire, the elongation of the spring and the strain energy stored in the spring when it is subjected to an axial tensile load of 50 N. What is the axial stiffness of this spring? Take G 82 GPa. Hints: Just use the formulas for shear stress, deflection and energy stored.