The Principle of Virtual Work states that for a system in static equilibrium:
Choose the correct answer
The actual work done by all forces equals zero
The virtual work done by all external forces and reactions on a virtual displacement consistent with constraints equals zero (sum of delta_W = 0)
Only internal forces do virtual work
Virtual work equals kinetic energy
Correct Answer
B. The virtual work done by all external forces and reactions on a virtual displacement consistent with constraints equals zero (sum of delta_W = 0)
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Principle of Virtual Work: for equilibrium, sum(F_i . delta_r_i) = 0 for any virtual displacement delta_r consistent with constraints. Useful for finding unknown reactions or forces without solving full equilibrium equations. Especially powerful for mechanisms and structural analysis (complementary virtual work for deflections).
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