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2-2 (b) Beams on supports

2-2 (b) Beams on supports

Point 9 of 12 — Parallel Coplanar Forces: Resultant and EquilibriumQuestion bank: 0 questions (0 with pictures)

09 2-2 (b) Beams on supports

Procedure

  • Draw all forces: weights (a uniform rod's weight acts at its midpoint), loads, reactions of supports, tensions.
  • Write "vertical forces balance".
  • Take moments about one support to find the other reaction directly.
✍️ Worked examples

Example 11:

  • A uniform wooden board, 6 m long, has mass 30 kg per metre.
  • It rests horizontally on supports at its ends A and B and a box of 240 kg·wt is on the board 4 m from B.
  • Find the reaction at each support.

Solution:

  • Mass of board =30×6=180 kg, so its weight is 180 kg·wt at the middle (3 m from each end).
  • Vertical balance: RA+RB=180+240=420.
  • Moments about B: RA×6=180×3+240×4=540+960=1500.
  • RA=250 kg·wt and RB=420−250=170 kg·wt.
  • As the box moves closer to A, RA increases and RB decreases.

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