If we use a link support in a structural system, how many unknowns would we have?
Try it first: pick an option, then read the explanation.
Correct answer: B. 1
Asked in SSC JE 29/01/2018 (Morning)
Detailed Explanation
Every support stops some kind of movement, and for each movement it stops it supplies one unknown reaction. Counting these unknowns tells us whether a structure can be solved by statics alone.
Why “1” Is Correct
A link is a short bar pinned at both ends. Because it is pinned at both ends, it can carry force only along its own axis. Its direction is known, so the only unknown is the magnitude of that force — one unknown. A roller behaves the same way, with its single reaction normal to the surface.
Why the Other Options Are Wrong
- A. 0: A support with zero unknowns would provide no restraint at all.
- C. 2: Two unknowns belong to a hinge (pin) support.
- D. None of these: The correct value, 1, is listed.
Key Point
Link or roller = 1 unknown; hinge = 2; fixed = 3.
Key Concepts for Students
- A link is a two-force member: force acts along the line joining its pins.
- Total unknowns are compared with 3 equations to judge determinacy of a planar body.
- Cables are also one-unknown supports, but act only in tension.
Practice more: this is question 1 in Force Analysis MCQs – Part 1. Try the whole set and check every answer instantly.