A closely coiled helical spring of round steel wire 2 mm in diameter has 8 complete coils of 16 mm mean radius. It is subjected to an axial load of 80 N. If the modulus of rigidity is 80 GPa, find the deflection of the spring.

A closely coiled helical spring made of 10 mm diameter steel wire has 15 coils of 100 mm mean diameter. If the modulus of rigidity G = 8.16 × 104 N/mm2, calculate the stiffness of the spring.

A closely coiled helical spring of stiffness 4 N/mm is connected in series with another spring of stiffness 6 N/mm. What is the equivalent stiffness of the composite spring?