Question

For two force members to be in equilibrium when _____________

(a) They both must not be collinear

(b) They must be of different magnitude

(c) They must be in the same direction

(d) They must be in the opposite direction cancelling each other

The question was asked at a job interview.

This interesting question is from Two and Three Force Members in chapter Equilibrium of a Rigid Body of Engineering Mechanics

Answer 1

Right choice is (d) They must be in the opposite direction cancelling each other

To explain I would say: Simply, for the equilibrium the net force must be zero. That is the forces must be collinear if equilibrium is to be established. And they must be in the opposite directions. They also must be of same magnitude, cancelling each other.