The 'virtual work principle' states that for a system in equilibrium, if it undergoes a virtual displacement:
Choose the correct answer
External work = 0 always
Virtual work of external forces = virtual internal strain energy for equilibrium (δW_ext = δW_int)
Stresses must be zero
Displacement must be real, not virtual
Correct Answer
B. Virtual work of external forces = virtual internal strain energy for equilibrium (δW_ext = δW_int)
Why is this the answer?
Principle of virtual work: for a system in equilibrium, the total virtual work done by all external forces through any compatible virtual displacement = virtual strain energy stored = 0 (for virtual work of external forces minus internal work). Used as: (1) equilibrium check; (2) computing deflections (unit load method). The virtual displacement must be kinematically admissible (compatible with constraints).
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