A close coil helical spring of mean diameter D consists of n coils of diameter d. If it carries an axial load W, the energy stored in the spring, is______________?

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A close coil helical spring of mean diameter D consists of n coils of diameter d. If it carries an axial load W, the energy stored in the spring, is______________?

A. 4WD²n/d4N
B. 4W²Dn/d4N
C. 4W²D3n/d4N(Correct)
D. 4W²D3n²/d4N