64. Pick up the incorrect statement from the following : The torsional resistance of a shaft is directly proportional to
A. modulus of rigidity
B. angle of twist
C. reciprocal of the length of the shaft
D. moment of inertia of the shaft section.

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65. If D and d are external and internal diameters of a circular shaft respectively, its polar moment of inertia, is
A. T(.2 (D4 d4)
B. T(4 (D4 d4)
C. 11 (D4 d4)
D. J.L. (D4 d4).

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66. A shaft rotating N.R.M. under a torque T, transmits a power
A. T/IN 30--30 Newton metres/sec
B.Newton metres/min
C.60--T 60 Newton metres/min
D.Newton metres/sec.

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67. If a solid shaft (diameter 20 cm, length 400 cm, N = 0.8 x 10 N/mm2) when subjected to a twisting moment, produces maximum shear stress of 50 N/mm2, the angle of twist in radians, is
A.0.001
B.0.002
C.0.0025
D.0.003

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68. A shaft subjected to a bending moment M and a torque T, experiences
A. maximum bending stress =ne
B. maximum shear stress = 16 T
C. both (a) and (b)
D. neither (a) nor (b).

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69.  Pick up the correct statement from the following :
A. The bending moment which when acting alone would produce the maximum stress equal to the major principal stress caused by combined bending and torsion, is called equivalent bending moment
B. Xs, = (M "I M2 + r2) where letters carry their usual meanings
C. Tcp Jm2 + T2 where letters carry their usual meanings
D. All the above.

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70.  Pick up the correct statement from the following :
A. A wire wound in spiral form, is called a helical spring
B. The pitch of a close coil spring, is very small
C. The angle made by the coil with horizontal, is called the angle of helix
D. All the above.

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