Shear Force and Bending Moment MCQ with answer and solution

Concept

Sign convention and rotation direction for shear force

Formula

Positive Shear = Left Up / Right Down (Clockwise Couple)

Step-by-step solution

1. By standard sign convention in structural analysis, positive shear force acts upward on the left side of a cut section and downward on the right side. 2. This equal and opposite vertical shear pair creates a clockwise turning moment on the beam element. 3. Consequently, positive shear force produces a clockwise rotation/couple on the left section. 4. Downward shear on the left represents negative shear convention. Answer: A

Explanation

By standard sign convention in structural analysis, positive shear force produces an upward shear force on the left side of a cut section and a downward shear force on the right side. This relative vertical shear force pair exerts a net clockwise turning tendency (rotation) on the isolated beam segment between the sections.

Why the other options are wrong

B) Downward force on the left of the cut represents negative shear convention. C) Anticlockwise moment corresponds to negative shear. D) Sagging describes positive bending moment, not shear force.

Shortcut

Positive shear = Up on left, down on right => Clockwise turning couple.

Common mistake

Confusing positive shear force (clockwise couple) with positive bending moment (sagging curvature).