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 close coil helical spring of mean diameter D consists of n coils of

1.	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.	<img src="/_files/images/civil-engineering/theory-of-structures/92-21-130-1.png">
B.	<img src="/_files/images/civil-engineering/theory-of-structures/92-21-130-2.png">
C.	<img src="/_files/images/civil-engineering/theory-of-structures/92-21-130-3.png">
D.	<img src="/_files/images/civil-engineering/theory-of-structures/92-21-130-4.png">
Answer» D. <img src="/_files/images/civil-engineering/theory-of-structures/92-21-130-4.png">