Force systems – classification of parallel forces Three forces of 100 N, 200 N, and 300 N are parallel but act in opposite directions to one another. What is the correct classification of such a system?

Introduction / Context:
Engineering mechanics classifies force systems by coplanarity, concurrency, and whether parallel forces act in the same or opposite directions. Correct classification helps choose the right resultant and equilibrium tools.

Given Data / Assumptions:

• Three forces: 100 N, 200 N, 300 N.
• Lines of action are parallel.
• Directions are opposed (not all the same way).
• All forces act in a single plane.

Concept / Approach:
Parallel forces acting in the same direction are called like parallel forces. When at least one force is opposite to the others, they are called unlike parallel forces. Concurrency is not applicable because parallel forces cannot meet at a single point unless they are collinear; typically they are non-concurrent, but the standard name for “opposite-direction parallel” is “unlike parallel forces”.

Step-by-Step Solution:

Verification / Alternative check:
Resultant of unlike parallel forces is obtained by vector addition along the common direction with appropriate signs; the line of action is located using the principle of moments—typical treatment for unlike parallel systems.

Why Other Options Are Wrong:

• coplanar concurrent: parallel forces do not pass through a common point.
• coplanar non-concurrent forces: true but incomplete; does not capture the “opposite directions” feature the question targets.
• like parallel forces: would require all forces in the same direction.

Common Pitfalls:
Confusing the broader classification (coplanar non-concurrent) with the specific term “unlike parallel forces”. Exams usually expect the specific term when directionality is emphasized.

Final Answer:
unlike parallel forces