Forces, Friction and Centroids
JKSSB Junior Engineer (Civil) · Mechanics and Structural Analysis · 5 practice questions with answers and explanations: 2 Easy, 3 Medium, 0 Hard.
Sample questions
Sample Easy question 1
Lami's theorem applies to:
- Two parallel forces
- Four non-coplanar forces
- Three concurrent forces in equilibrium
- A single force
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Answer: C. Each force is proportional to the sine of the angle between the other two.
Sample Easy question 2
The centroid of a semicircle of radius R from its diameter is at a distance of:
- R ÷ π
- 4R ÷ 3π
- R ÷ 2
- 2R ÷ 3
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Answer: B. This is about 0.424 R.
Sample Medium question 3
Two forces of 3 N and 4 N act at a point at right angles to each other. Their resultant is:
- 7 N
- 12 N
- 1 N
- 5 N
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Answer: D. R = √(3² + 4²) = 5 N.
Sample Medium question 4
A force of 20 N acts at a perpendicular distance of 0.5 m from a point. Its moment about the point is:
- 40 N·m
- 10 N·m
- 20.5 N·m
- 2.5 N·m
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Answer: B. Moment = force × perpendicular distance.
Sample Medium question 5
A block of weight 500 N rests on a horizontal plane with a coefficient of friction of 0.3. The horizontal force needed to start it sliding is:
- 15 N
- 1,667 N
- 150 N
- 500 N
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Answer: C. F = μ N = 0.3 × 500 = 150 N.