JAMB Physics 1992 Question 7

Question 7

Equilibrium of Forces

A uniform light rod is kept in horizontal equilibrium under the influence of four forces as shown above. Which of the following equations correctly represents the condition of equilibrium for the rod?

A.F₁ + F₂ = F₃ + F₄
B.F₁ + F₂ − F₃ + F₄ = 0
C.(F₁ + F₂)ab = (F₃ + F₄)cd
D.F₁a + F₂b − F₃c − F₄d = 0

Show the answer and explanation

Answer: D (F₁a + F₂b − F₃c − F₄d = 0)

Explanation

Take moments about the pivot: F₁ and F₂ turn the rod one way, F₃ and F₄ the other way. Balance means F₁a + F₂b = F₃c + F₄d.