Lever balance: weight on the other arm

On a lever, a 2 kg object hangs 0.3 m to the left of the fulcrum. What weight must hang 0.6 m to the right of the fulcrum to balance the lever? (Take g = 10 N/kg.)

Step-by-step

1. Weight on the left F₁ = mg = 2×10 = 20
   The object's weight provides the effort on the left
2. F₁·L₁ = F₂·L₂ → F₂ = F₁×L₁/L₂ = 20×0.3/0.6 = 10
   Lever balance: effort × effort arm = load × load arm
3. Equivalent mass = 10/10 = 1 kg
   Convert to the everyday "how heavy"

Why it works

A lever balances when the effort times its arm equals the load times its arm: F₁ × L₁ = F₂ × L₂. A longer arm therefore needs a smaller force.

Common mistakes

• Multiplying by 0.6 ÷ 0.3 instead of dividing by it.
• Forgetting to turn the 2 kg mass into a weight of 20 N first.

Related

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