31. A steel rod 15 m long Is at a temperature of 15 °C. The values of α = 12 × 10^{-6} /°C and E = 200 GN/m^{2} are adopted. When the temperature is raised to 65°C, what is the free expansion of the length; and if this expansion of the rod is fully prevented, what is the temperature stress produced?

- 5 mm and 120 MN/m
^{2} - 9 mm and 120 MN/m
^{2} - 5 mm and 150 MN/m
^{2} - 9 mm and 150 MN/m
^{2}

32. A steel rod of length 20 m at 30°C is heated upto 40°C. What is the temperature stress developed if the expansion is prevented?

Given, α =12 x 10^{-6} per °C, E = 2 × 10^{5} N/mm^{2}

- 24 N/mm
^{2} - 2.4 N/mm
^{2} - 0.24 N/mm
^{2} - 240 N/mm
^{2}

33. Stress is

- a measure of deformation of material
- resistance to forces resulting in elongation
- internal force exerted by neighbouring particles over each other
- resistance to bending and torsion

34. A bar of brass is enclosed in a steel tube and is rigidly fastened at both the ends. If the coefficient of thermal expansion of brass is more than that of steel, when temperature rises, the nature of stresses developed are

- tensile in steel tube and compressive in brass bar
- compressive in steel tube and tensile in brass bar
- tensile in both steel tube and brass bar
- compressive in both steel tube and brass bar

35. The stress developed due to external force in an elastic material

- Depends on elastic constant
- Does not depend on elastic constant
- Depends partially on elastic constant
- Depends on limit of proportionality

36. Two roads of different materials having coefficient of linear expansion α_{1} , α_{2 }and Young’s modulus E_{1}, E_{2} respectively are fixed between two massive walls. The rods are heated such that they undergo the same increase in temperature. There is no bending of the rods. If α_{1} : α_{2} = 2 : 3, the thermal stresses are equal, what is the ratio of E_{1} to E_{2}?

- 1:1
- 2:3
- 4:9
- 3:2

37. When a nut is tightened on the bolt the nature of stress in the bolt is

- tensile
- compressive
- shearing
- bending

38. A copper rod of square cross-section is fixed between two rigid supports and over which a steel rod of square cross-section is simply placed. If the temperature of the whole assembly is raise T°C, the stresses in steel and copper respectively are

- tensile and compressive
- zero and compressive
- compressive and tensile
- compressive and zero

39. A metal bar of length 100 mm is inserted between two rigid supports and its temperature is increased by 10°C. If the coefficient of thermal expansion is 8 x 10^{-6} per °C and the young’s modulus is 1.5 x 10^{5} MPa, the stress in the bar is

- Zero
- 12 MPa
- 24 MPa
- 2400 MPa

40. When a body is subjected to two equal and opposite pulls, as a result of which the body tends to extend its length, the stress and strain induced is

- Compressive stress, tensile strain
- Tensile stress, compressive strain
- Compressive stress, compressive stran
- Tensile stress, tensile strain