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JAMB Physics 1986 Question 10

Question 10

Equilibrium of Forces

In Fig. 3, the three forces F1, F2, F3 acting at O are in equilibrium. If the magnitude of F1 is 10.0 N and the magnitude of F2 is 5.0 N, find the magnitude of F3.

Diagram for this question
  1. A.26.4 N
  2. B.15.0 N
  3. C.13.2 N
  4. D.10.0 N
Show the answer and explanation

Answer: C (13.2 N)

Explanation

F3 balances the resultant of F1 and F2, which are 60° apart: R² = 10² + 5² + 2 × 10 × 5 × cos 60° = 175, so R ≈ 13.2 N.