Lever: 1.5 kg at 0.6 m, mass at 0.3 m

A 1.5 kg object hangs 0.6 m to the left of the fulcrum of a lever. What mass must hang 0.3 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 = 1.5×10 = 15
   The object's weight provides the effort on the left
2. F₁·L₁ = F₂·L₂ → F₂ = F₁×L₁/L₂ = 15×0.6/0.3 = 30
   Lever balance: effort × effort arm = load × load arm
3. Equivalent mass = 30/10 = 3 kg
   Convert to the everyday "how heavy"

Why it works

The lever balances when F₁ × L₁ = F₂ × L₂, so the two forces are inversely proportional to their arms. Halving the arm doubles the force needed.

Common mistakes

• Multiplying 15 N by 0.3 ÷ 0.6 instead of dividing by it.
• Answering 0.75 kg by assuming the mass and the arm are proportional.

Related

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