Question

A close helical spring of 100 mm mean diameter is made of 10 mm diameter rod, and has 20 turns. The springs carries an axial load of 200 kN with $G=8.4\times {10}^{4}N/m{m}^2$. The stiffness of the spring is nearly

• A. 5.25 N/mm
• B. 6.50 N/mm
• C. 7.25 N/mm
• D. 8.50 N/mm

Answer 1

The correct option is A 5.25 N/mm

$k=\frac{W}{\delta }=\frac{G{d}^4}{64R^{3}n}=\frac{8.4\times {10}^4\times {10}^4}{64\times {\left(\frac{100}{2}\right)}^3\times 20}=5.25N/mm$