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UPSC Civil Service Exam Questions - Engineering

Q1:

A circular shaft subjected to torsion undergoes a twist of 1° in a length of 120 cm. If the maximum shear stress induced is limited to 1000 kg/cm2 and if modulus of rigidity G = 0.8 x 106 kg/cm2, then the radius of the shaft should be

A π/18

B 18/π

C π/27

D 27/π

ANS:D - 27/π

from The Torsion Equation we have,
T/J=GO/L=Fs/R here consider only GO/L= Fs/R,
From the data we have theta = 1, l = 120cm, toue = 1000kg/cm^2 and G = 0.8 X 10^6,
0.8 x 10^6 x 1/120 = 1000/R then Radius of shaft R = 27/3.142(Phi).