A close-coiled helical spring has a mean diameter of 105 mm and 18 coils of wire of diameter 10 mm. Find the maximum stress in the wire, the increase in the number of turns, and the total rotation...

A close-coiled helical spring has a mean diameter of 105 mm and 18 coils of wire of diameter 10 mm. Find the maximum stress in the wire, the increase in the number of turns, and the total rotation when the coil is subjected to an axial twist of 1.2 Nm. E = 200 GPa.