BCE Mechanics of Materials 2

Question 1

In the flexure formula σ = My/I, what does the variable 'y' represent?

Accepted Answer

The distance from the neutral axis to the point of interest

Answer

In the bending stress formula, y is the perpendicular distance from the neutral axis to the fiber where stress is being calculated.

Question 2

For a simply supported beam of span L carrying a central point load W, the maximum bending moment is:

Accepted Answer

WL/4

Answer

Each reaction is W/2; the maximum moment at midspan = (W/2)(L/2) = WL/4.

Question 3

The section modulus Z of a solid rectangular section (width b, height h) is:

Accepted Answer

bh²/6

Answer

Z = I / y_max = (bh³/12) / (h/2) = bh²/6; it directly gives maximum bending stress as σ = M/Z.

Question 4

For a rectangular beam cross-section, where does the maximum shear stress due to transverse loading occur?

Accepted Answer

At the neutral axis

Answer

Shear stress is zero at the free (extreme) surfaces and reaches its maximum at the neutral axis for a rectangular section.

Question 5

The second moment of area (moment of inertia) of a solid circular cross-section with diameter D about a centroidal axis is:

Accepted Answer

πD⁴/64

Answer

I = πD⁴/64 for a solid circle about a diameter; the polar moment of inertia J = 2I = πD⁴/32.

BCE - Bachelor of Civil Engineering Practice Test