Question

Which of the following needs to zero for the stability of equilibrium configuration?

(a) ∑F=0, ∑M=0 and ∑θ = 0

(b) ∑F=0, ∑M≠0 and ∑θ = 0

(c) ∑F≠0, ∑M=0 and ∑θ = 0

(d) ∑F=0, ∑M=0 and ∑θ≠0

This question was posed to me in an interview for job.

My question is from Stability of Equilibrium Configurations topic in chapter Principle of Virtual Work of Engineering Mechanics

Answer 1

Right answer is (d) ∑F=0, ∑M=0 and ∑θ≠0

For explanation I would say: The summation of the forces needs to be zero. So does the summation of the moments need to zero. But talking about the angles, they not need to zero. But the forces which are acting at particular angles, must needed to be equal to zero. The basic need of the forces to make the body in equilibrium.