System of forces — forces whose lines of action intersect at a single point but lie in different planes are termed:

Introduction / Context:
Classifying force systems helps select appropriate equilibrium equations. In three dimensions, concurrency (meeting at a point) and coplanarity (lying in one plane) are independent attributes. Recognizing a non-coplanar concurrent system allows simplification to moment sums about the intersection point along with vector force balance.

Given Data / Assumptions:

• All forces intersect at a common point.
• Their lines of action are not confined to a single plane.

Concept / Approach:

Concurrent implies a single intersection point; non-coplanar implies three-dimensional arrangement. Such systems are solvable using ΣF = 0 in vector form without needing separate couple-moment equations about arbitrary origins (since moments about the concurrency point from each force are zero).

Step-by-Step Solution:

Verification / Alternative check:

Drawing skew lines converging at a point confirms three-dimensional geometry with concurrency.

Why Other Options Are Wrong:

Coplanar non-concurrent: either coplanar or non-concurrent is violated. Non-coplanar non-concurrent do not meet at one point. “Intersecting forces (same plane)” contradict non-coplanarity.

Common Pitfalls:

Confusing skew lines with parallel forces; assuming concurrency implies coplanarity.

Final Answer:

non-coplanar concurrent forces