Chapter-12
Spring
S K Mondal’s
Reason (R): Winding in opposite directions prevents locking of the two coils in case of misalignment or buckling. [IAS-1996] (a) Both A and R are individually true and R is the correct explanation of A (b) Both A and R are individually true but R is NOT the correct explanation of A (c) A is true but R is false (d) A is false but R is true IAS-1. Ans. (a) IAS-2.
An open-coiled helical spring of mean diameter D, number of coils N and wire diameter d is subjected to an axial force' P. The wire of the spring is subject to: [IAS-1995] (a) direct shear only (b) combined shear and bending only (c) combined shear, bending and twisting (d) combined shear and twisting only IAS-2. Ans. (d) IAS-3.
Assertion (A): Two concentric helical springs used to provide greater spring force are wound in opposite directions. [IES-1995; IAS-2004] Reason (R): The winding in opposite directions in the case of helical springs prevents buckling. (a) Both A and R are individually true and R is the correct explanation of A (b) Both A and R are individually true but R is NOT the correct explanation of A (c) A is true but R is false (d) A is false but R is true IAS-3. Ans. (c) It is for preventing locking not for buckling. IAS-4. Which one of the following statements is correct? [IES-1996; 2007; IAS-1997] If a helical spring is halved in length, its spring stiffness (a) Remains same (b) Halves (c) Doubles (d) Triples Gd4 1 so k ∞ andn wiil behalf IAS-4. Ans. (c) Stiffness of sprin ( k ) = n 8D3n IAS-5.
A closed coil helical spring has 15 coils. If five coils of this spring are removed by cutting, the stiffness of the modified spring will: [IAS-2004] (a) Increase to 2.5 times (b) Increase to 1.5 times (c) Reduce to 0.66 times (d) Remain unaffected
IAS-5. Ans. (b) K= IAS-6.
Gd 4 8D3 N
or K α
K N 15 1 or 2 = 1 = = 1.5 N K1 N 2 10
A close-coiled helical spring has wire diameter 10 mm and spring index 5. If the spring contains 10 turns, then the length of the spring wire would be: [IAS-2000] (a) 100 mm (b) 157 mm (c) 500 mm (d) 1570 mm
IAS-6. Ans. (d) l = π Dn = π ( cd ) n = π × ( 5 × 10 ) ×10 = 1570 mm IAS-7.
Consider the following types of stresses: [IAS-1996] 1. torsional shear 2. Transverse direct shear 3. Bending stress The stresses, that are produced in the wire of a close-coiled helical spring subjected to an axial load, would include (a) 1 and 3 (b) 1 and 2 (c) 2 and 3 (d) 1, 2 and 3 IAS-7. Ans. (b) IAS-8.
Two close-coiled springs are subjected to the same axial force. If the second spring has four times the coil diameter, double the wire diameter and double the number of coils of the first spring, then the ratio of deflection of the second spring to that of the first will be: [IAS-1998] 1 (a) 8 (b) 2 (c) (d) 1/16 2
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