A close coil helical spring when subjected to a moment M having its axis along the axis of the helix A. It is subjected to pure bending B. Its mean diameter will decrease C. Its number of coils will increase D. All the above

The correct answer is D. All the above.

A close coil helical spring when subjected to a moment M having its axis along the axis of the helix will be subjected to pure bending. This is because the moment will cause the spring to bend about its axis, and the only force acting on the spring will be the bending moment. The mean diameter of the spring will decrease as it bends, and the number of coils will increase as the spring stretches.

The following is a more detailed explanation of each option:

• Option A: A close coil helical spring when subjected to a moment M having its axis along the axis of the helix will be subjected to pure bending. This is because the moment will cause the spring to bend about its axis, and the only force acting on the spring will be the bending moment.
• Option B: The mean diameter of the spring will decrease as it bends. This is because the bending moment will cause the spring to stretch, and the stretching will cause the coils to get closer together.
• Option C: The number of coils will increase as the spring stretches. This is because the stretching will cause the coils to get closer together, and the closer coils will form more coils.

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