Question

The figure shows a uniform metre rule placed on a fulcrum at its mid-point O and having a weight 40 gf at the 10 cm mark and a weight of 20 gf at the 90 cm mark.

1. Is the metre rule in equilibrium? If not how will the rule turn?
2. How can the rule be brought in equilibrium by using an additional weight of 40 gf?

Answer 1

W₁ × d₁ = W₂ × d₂

40 × 40 = 20 × 40

1600 ≠ 800

Anticlockwise moment ≠ clockwise moment

1. No, the rule will turn anticlockwise
   Anticlockwise moment > clockwise moment.
2. Moment of force needed = 800
   Where 40 gf additional should be placed
   1600 = 800 + 40 × d
   ∴ 40d = 1600 − 800 = 800
   d = `800/40 = 20` cm