# Machine Design Questions and Answers – Concentric & Spiral Springs

This set of Machine Design Multiple Choice Questions & Answers (MCQs) focuses on “Concentric & Spiral Springs”.

1. In concentric springs, vibrations called surge are amplified.
a) True
b) False

Explanation: Surge are eliminated.

2. Can concentric springs be used to obtain a force which is not proportional to its deflection?
a) True
b) False

Explanation: Two sprigs having different free length can be meshed to obtain such a result.

3. The load shared by each spring is inversely proportional to the cross section of wire.
a) Yes
b) No, it is directly proportional
c) It is proportional to its square
d) It is proportional to its square root

Explanation: It is directly proportional to the cross section of wire.

4. A concentric spring consists of 2 sprigs of diameter 10mm and 4mm. The net force acting on the composite spring is 5000N. Find the force acting on each of the two springs.
a) 1232.2N and 3767.8N
b) 786.4N and 4213.6N
c) 689.7N and 4310.3N
d) 645.3N and 4354.7N

Explanation: P₁/P₂=d₁²/d₂² and P₁+P₂=5000.

5. If the spring have same solid length and number of coils in the two springs are 8 and 10, then find the diameter of the spring with 8 coils. It is given diameter of spring with 10 coils is 12mm.
a) 9.6mm
b) 9mm
c) 12mm
d) 15mm

Explanation: N₁d₁=N₂d₂.
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6. Two spring having stiffness constants of 22N/mm and 25N/mm are connected in parallel. They are to be replaced by a single spring to have same effect. The stiffness of that spring will be?
a) None of the mentioned.
b) 3N/mm
c) 47N/mm
d) 11.7N/mm

Explanation: k=22+25.

7. What will happen if stresses induced due to surge in the spring exceeds the endurance limit stress of the spring.
a) Fatigue Failure
b) Fracture
c) None of the listed
d) Nipping

Explanation: If endurance limit is passed, fatigue failure will follow.

8. Surge is caused by resonance effect in the spring.
a) True
b) False

Explanation: When the natural frequency of vibrations of the spring coincides with frequency of external periodic force, resonance occurs.

9. Surge is a desirable effect in the sprigs.
a) True
b) False

Explanation: Surge means vibratory motion which isn’t welcomed anywhere in the machinery.

10. For a helical torsion sprig, the stress concentration factor at inner fibre is? Give spring index=5.
a) 1.005
b) 1.175
c) 1.223
d) 1.545

Explanation: K=4C²-C-1/4C(C-1).

11. For a helical torsion sprig, the stress concentration factor at outer fibre is? Give spring index=5.
a) 0.78
b) 0.87
c) 1.87
d) 0.69

Explanation: K=4C²+C-1/4C(C+1).

12. Spiral spring is quite rigid.
a) Yes
b) No it is flexible
c) It is of moderate rigidity
d) Rigidity can’t be determined

Explanation: Spiral spring is made of very thin wire which imparts great flexibility.

13. The strip of spiral spring is never subjected to pure bending moment.
a) True
b) False

Explanation: The strip of spiral spring is subjected to pure bending moment.

14. Calculate the bending stress induced in the strip of the helical spring. The spring is subjected to a moment of 1250N-mm with breadth and thickens of the strip being 11mm and 1.5mmm respectively.
a) 508.8N/mm²
b) 612.2N/mm²
c) 606.1N/mm²
d) 564.3N/mm²

Explanation: σ=12M/bt².

15. Angle of rotation o arbour with respect to drum is given by?
a) None of the listed
b) 12ML/Ebtᵌ
c) 8 ML/Ebtᵌ
d) 16ML/Ebtᵌ

Explanation: θ=ML/EI where I=btᵌ/12.

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