which of the below conditions must hold for a body acted upon by a system of three coplanar forces equilibrium?

I. All the three forces must be concurrent.
II. The upward force is equal to the downward force.
III. The algebraic sum of the moment about any point must be zero.

A. I and II only
B. I and III only
C. II and III only
D. I, II and III

Correct Answer:

Option B = I and III only

Explanation

Condition (ii) is a condition for an equilibrium of parallel forces only while conditions (i) and (iii) are correct for both parallel and non- parallel coplanar forces.