Three coplanar forces keep a rigid body in equilibrium, and no two forces are parallel. What geometric condition must they satisfy?
Correct answer: D. Their lines of action are concurrent
- A. Their lines of action are equally spaced
- B. Their lines of action are perpendicular
- C. Their magnitudes are identical
- D. Their lines of action are concurrent
Explanation
For three nonparallel coplanar forces to have zero resultant moment, their lines of action must meet at one point. Equal magnitudes or perpendicular directions are not required for equilibrium.
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Structural analysis determines how beams, frames, trusses and arches carry loads through reactions, shear forces, bending moments, axial forces and deflections. It covers free-body diagrams, equilibrium equations, determinacy, influence lines and methods such as slope deflection, moment distribution and virtual work, while distinguishing analysis of a structure from its design.
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