The 3D equation of equilibrium in a body (without body forces) is:

Question

Accepted Answer

C. {'text': '∂σ_ij/∂x_j = 0 — divergence of stress tensor vanishes (Cauchy)', 'label': 'B'}

For an infinitesimal element in static equilibrium without body forces (gravity, etc.), the sum of internal-force contributions from neighboring elements must balance: $\partial \sigma_{ij}/\partial x_j = 0$ (j summed via Einstein notation).

Answer

{'text': 'σ_ij = ε_ij', 'label': 'C'}

Answer

{'text': 'σ_ij = const', 'label': 'A'}

Answer

{'text': '∇·u = 0', 'label': 'D'}