A closely coiled helical spring made 10 mm diameter steel wire has 15 coils of 100 mm mean diameter. The spring is subjected to an axial load of 100 N. calculate the stiffness of the spring. (Take modulus of rigidity, C = 8.16 × 104 N/mm2)
1
5.461 N/mm
2
680 N/m
3
4.210 N/mm
4
6.80 N/mm