GATE 2018 ME (ME1) – Question 31
A compression helical spring’s wire diameter increases by 2%. The change in stiffness, to two decimals, is ______%.
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Correct answer: 8.00 to 8.50
Explanation
For unchanged coil geometry and material, spring stiffness is proportional to wire diameter to the fourth power. Increase is $100[(1.02)^4-1]=8.24\%$. The 8% differential approximation omits higher powers.