Question

What is the maximum number of times the pathlines of two particles can intersect in an one dimensional flow?

(a) 0

(b) 1

(c) 2

(d) infinite

The question was asked during an interview for a job.

This interesting question is from Types of Flow Lines topic in section Kinematics of Flow and Ideal Flow of Fluid Mechanics

Answer 1

The correct option is (b) 1

For explanation I would say: The pathline of a particle in an one-dimensional flow is a straight line along the direction it moves. When two particles move in the same direction, their pathline will never intersect and when they move in different directions, their pathlines will intersect only once.