Question

If the body is in equilibrium, but it having a rotational curled ray shown in the free body diagram then:

(a) The diagram is wrong

(b) Such rotations can’t be shown in the fbds(free body diagrams)

(c) The ray shown may be correct, but the body is not said to be in equilibrium

(d) The body is said to be in equilibrium only, as the other forces will cancel out that rotation and the network done will be zero

This question was addressed to me during an online interview.

Origin of the question is Work topic in chapter Principle of Virtual Work of Engineering Mechanics

Answer 1

Correct choice is (d) The body is said to be in equilibrium only, as the other forces will cancel out that rotation and the network done will be zero

To elaborate: The body having equilibrium will not rotate at any cost. Yes, the diagram may contain the rotational array showing the couple being acted over the structure. But the thing is that the forces, i.e. the other forces which are outside the dependency of this rotation will cancel out this rotation and thus the body is in equilibrium.