Member Force Under a Hanging Load

Mediumtrussesmethod of joints
A 10 kN vertical load hangs from a joint supported by two identical members, each inclined 45° from the horizontal and symmetric about the vertical. What is the axial force in each member?
  1. A7.07 kN
  2. B5 kN
  3. C10 kN
  4. D14.1 kN
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Answer: A. 7.07 kN

Method of joints at the loaded joint: ΣFy = 0 → 2 · F · sin 45° = 10 → F = 10 / (2 · 0.707) = 7.07 kN. Horizontal components cancel by symmetry. 5 kN forgets the sine; 14.1 kN uses 10/sin45° without splitting between two members.
kN
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