Resultants of coplanar non-concurrent forces If a rigid body is acted upon by several coplanar non-concurrent forces, the resulting motion may be which of the following?

Difficulty: Easy

Correct Answer: All of these

Explanation:


Introduction / Context:
Understanding how a general system of coplanar non-concurrent forces affects a rigid body is key to predicting motion or ensuring equilibrium in structures and mechanisms.



Given Data / Assumptions:

  • Forces lie in a single plane but their lines of action do not meet at one point (non-concurrent).
  • Rigid-body assumptions; Newtonian mechanics.


Concept / Approach:
A general planar force system can be reduced to a single resultant force and a resultant moment (couple). Depending on whether the net force and/or net moment vanish, the body may translate and rotate (general plane motion), rotate without translation (pure couple), or remain at rest (complete equilibrium).



Step-by-Step Solution:

Compute ΣF_x, ΣF_y, and ΣM_O.If ΣF ≠ 0 and ΣM ≠ 0 → general plane motion (translation + rotation).If ΣF = 0 and ΣM ≠ 0 → pure rotation due to a couple.If ΣF = 0 and ΣM = 0 → complete equilibrium (no motion).


Verification / Alternative check:
Equivalent system reduction (force–couple) always exists in the plane; Chasles’ theorem supports decomposition into translation plus rotation.



Why Other Options Are Wrong:

  • Each of A, B, C is possible under specific resultant conditions; hence the combined option “All of these” is correct.
  • “Only translation without any rotation” is not guaranteed for non-concurrent systems; a net couple generally exists.


Common Pitfalls:
Assuming non-concurrent forces must always cause rotation; if arranged to cancel moments, pure translation can occur, but that requires special geometry.



Final Answer:
All of these


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