Shear Force at the Free End — Cantilever with Uniformly Distributed Load A cantilever beam of length l carries a uniformly distributed load w per unit length over the entire span. The shear force at the free end is:
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Azero
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Bw l / 4
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Cw l / 2
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Dw l
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E2 w l
Answer
Correct Answer: zero
Explanation
Introduction:Shear force and bending moment diagrams for basic loading cases are core knowledge in strength of materials. For a cantilever with a uniformly distributed load (UDL), recognizing boundary values helps draw accurate diagrams quickly.
Given Data / Assumptions:
- Cantilever span length = l, fixed at one end and free at the other.
- Uniformly distributed load w acts over the entire length.
- Linearly elastic, small deflection assumptions.
Concept / Approach:Shear force is the integral of load intensity, and the bending moment gradient equals shear. At the free end of a cantilever, there is no support reaction to carry shear; thus the internal shear at that section must be zero. Maximum shear occurs at the fixed support where reactions develop.
Step-by-Step Solution:1) Resultant of UDL = w * l acting at midspan from the free end.2) Shear diagram for a cantilever with UDL starts at V = w * l at the fixed end and linearly decreases to V = 0 at the free end.3) Therefore, shear at the free end is zero.
Verification / Alternative check:From boundary conditions, the free end cannot develop internal shear or moment; both must be zero at that free boundary.
Why Other Options Are Wrong:
- w l, w l / 2, w l / 4, 2 w l: These are nonzero values that contradict the cantilever free-end condition.
Common Pitfalls:Confusing the fixed-end values (nonzero) with the free-end values (zero for both V and M).
Final Answer:zero