A prismatic bar has a cross section of 25 mm × 50 mm and a length of 2 m. If the bar is subjected to an axial tensile force of 90 kN, the bar is elongated by 1.5 mm. What is the tensile stress?

Concept:

\(σ = E\times e\)

\(Stress(σ) ={ Force (F)\over Cross\,sectional\,Area(A)}\)

Where E = modulus of elasticity, e = strain.

Calculation:

Given

Cross-section of prismatic bar = 25 mm × 50 mm

Length (L) = 2 m

Axial tensile force (F) = 90 kN or 90000 N

Elongation (ΔL) = 1.5 mm

Tensile stress (σ) = \(Tensile\,Force (F)\over Cross\, sectional\, area (A)\) = \({90000\over 25\times 50}=72 \, N/mm^2\)

Tensile stress (σ) = 72 N/mm²

Hence option (4) is the correct answer.