STRENGTH OF MATERIAL

A cylindrical bar of 1 m length deforms by 1 mm under axial load. What is the strain in the bar?

• 0.11
• 0.001
• 0.01
• 0.5

Answer explanation

Strain = Deformation / Original length = 0.001 m / 1 m = 0.001.

A wire of diameter 1 mm is bent into a circular arc of radius 1 m. If Young’s modulus is 100 GPa, what is the maximum tensile stress?

• 0.05 GPa
• 0.1 GPa
• 0.25 GPa
• 0.5 GPa

Answer explanation

σ = E*y/R = (100×10³)*(0.5)/1000 = 50 MPa = 0.05 GPa.

If a cantilever of length L carries a UDL (w) from free end to fixed end, maximum bending moment at fixed end is:

• wL
• wL²/2
• wL²/3
• wL²/6

Answer explanation

For cantilever with UDL over full length, M = wL²/2 at fixed end.

A beam has breadth b and depth d. Its moment of inertia is:

• bd²/6
• bd²/8
• bd³/12
• bd³/8

Answer explanation

Moment of Inertia of rectangle about base = bd³/12.

A rectangular beam cut from circular log (diameter D). What is the depth of strongest beam?

• 0.5D
• 0.707D
• 0.816D

• 0.75D

Answer explanation

For maximum section modulus, depth = √2/3 * D = 0.816 D.

If a point load W is applied at free end of cantilever of length L, what is the maximum bending moment?

• WL
• WL/2
• WL²/2
• WL²

Answer explanation

Max bending moment at fixed end = W × L.

A beam has cross-section with I = 8×10⁶ mm⁴, y = 100 mm, M = 4 kNm. What is bending stress?

• 5 MPa
• 50 MPa
• 0.5 MPa
• 10 MPa

Answer explanation

σ = My/I = (4×10⁶)(100)/(8×10⁶) = 50 MPa.

If section modulus Z = 2×10⁶ mm³ and bending moment is 4×10⁶ Nmm, what is maximum stress?

• 1 MPa
• 2 MPa
• 3 MPa
• 4 MPa

Answer explanation

σ = M/Z = 4×10⁶ / 2×10⁶ = 2 N/mm² = 2 MPa.

A mild steel specimen of length 300 mm elongates by 1.5 mm under a load. What is the strain?

• 0.005
• 0.001
• 0.0005
• 0.003

Answer explanation

Strain = ΔL / L = 1.5 / 300 = 0.005.

In a beam, section modulus increases. What happens to bending stress for same moment?

• Increases
• Decreases
• Remains same
• Zero

Answer explanation

σ = M/Z. As Z increases, σ decreases.