Question

If the secondary couple polygon is open and the force polygon is closed then stability is achieved.

(a) True

(b) False

The question was posed to me at a job interview.

This interesting question is from Balancing of Coupled Locomotives & Secondary Forces of Multi-cylinder Inline Engines topic in section Balancing of Reciprocating Masses of Machine Dynamics

Answer 1

Correct answer is (b) False

To explain I would say: In order to achieve stability, the sum of secondary forces and secondary couples must be zero and their respective polygons must be closed.