For a cantilever beam, the internal shear force and bending moment at the free end are zero. Considering the listed load cases, when is this statement true?

Difficulty: Easy

Correct Answer: None of the above (it is always true for the free end of a cantilever)

Explanation:


Introduction / Context:
Cantilever beams are fixed at one end and free at the other. Understanding boundary conditions—especially that the free end cannot transmit moment or shear—is crucial for drawing correct shear-force and bending-moment diagrams.



Given Data / Assumptions:

  • Cantilever of any prismatic or non-prismatic form.
  • Loads may be a point load, uniformly distributed load, or other distributions.
  • Linear elastic beam theory applies for internal force definitions.


Concept / Approach:
By definition, at the free end of a cantilever, there is no support to develop a reaction shear or reaction moment. Therefore, the internal shear force V and bending moment M evaluated at the very free tip are zero for any applied loading configuration.



Step-by-Step Solution:

Cut a free-body section at the free end and shrink its length to zero.Since no support exists at the tip, the section cannot develop internal V or M at the end point.Consequently, V_free = 0 and M_free = 0 irrespective of load distribution along the span.


Verification / Alternative check:
All standard shear and moment diagrams for cantilevers start at zero at the free end and grow towards the fixed end to meet boundary conditions at the built-in support.



Why Other Options Are Wrong:
Options limiting the zero condition to particular loads (point load or UDL) are incorrect; the zero condition holds universally at the free end.“True only for no loading” is false; even with loads, the free-end values remain zero.



Common Pitfalls:
Misreading internal shear/moment at a small distance from the tip (which may be nonzero) versus exactly at the tip where both are zero.



Final Answer:

None of the above (it is always true for the free end of a cantilever)

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