BCE Mechanics of Materials

Question 1

What is the SI unit of stress?

Accepted Answer

Pascal (Pa)

Answer

Stress is force per unit area; in SI units, 1 Pa = 1 N/m², which is the standard unit for stress.

Question 2

Hooke's Law states that stress is proportional to strain within the elastic limit. The constant of proportionality is called the:

Accepted Answer

Modulus of elasticity (Young's modulus)

Answer

Young's modulus E is the proportionality constant in Hooke's Law (σ = Eε) relating normal stress to normal strain in the elastic range.

Question 3

A steel rod with a cross-sectional area of 500 mm² is subjected to an axial tensile load of 100 kN. What is the tensile stress?

Accepted Answer

200 MPa

Answer

Stress σ = P/A = 100,000 N / 500 mm² = 200 N/mm² = 200 MPa.

Question 4

Poisson's ratio (ν) is defined as the ratio of:

Accepted Answer

Lateral strain to longitudinal strain

Answer

Poisson's ratio ν = –(lateral strain / longitudinal strain); the negative sign accounts for the opposite sense of the strains.

Question 5

Beyond the elastic limit of a material, what occurs when the load is removed?

Accepted Answer

Permanent (plastic) deformation remains

Answer

The elastic limit is the maximum stress below which a material fully recovers; beyond it, permanent plastic deformation is retained after unloading.

BCE - Bachelor of Civil Engineering Practice Test