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UPSC Civil Service Exam Questions - Engineering

Q1:

A 600 mm long and 50 mm diameter rod of steel (E = 200 GPa, α = 12 x 10-6/°C) is attached at the ends to unyielding supports. When the temperature is 30°C there is no stress in the rod. After the temperature of the rod drops to - 20°C, the axial stress in the rod will be

A 24 MPa (compressive)

B 72 MPa (compressive)

C 120 MPa (tensile)

D 144 MPa (compressive)

ANS:C - 120 MPa (tensile)

Thermal stress = ax(T2-T1)xE.
12x10^-6(-50)x200x10^9.
= -120Mpa
Attached at the ends to unyielding supports;
So, tensile stress.