A door is opened by pushing on the handle, which is positioned at the edge of the door, far from the hinges. Explain why pushing on the handle near the edge of the door requires less force than pushing at a point close to the hinges, and state what would happen to the moment if the applied force were doubled while keeping the distance from the pivot the same.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
The moment (torque) about the hinges is given by \(M=F\,r\sin\theta\). The handle is pushed perpendicular to the door, so \(\sin\theta=1\) and \(M=F\,r\).\n1. The distance \(r\) from the hinges to the handle is greatest at the edge of the door.\n2. A larger \(r\) means a smaller force \(F\) is required to give the same moment.\n3. Near the hinges \(r\) is very small, so a much larger force is needed for the same moment.\n4. If the force is doubled while \(r\) stays the same, the moment doubles because \(M\propto F\).
Examiner tips
- Show the torque formula and note that the force is perpendicular so sinθ=1.
- Explain the effect of a larger distance on the required force.
- State that doubling the force doubles the moment, keeping distance constant.
Common mistakes
- Using the wrong formula (e.g. force × angle instead of distance).
- Ignoring that the force is perpendicular and treating sinθ as variable.
- Failing to state the effect of doubling the force on the moment.
Mark scheme (4 marks)
- The moment depends on both the force and the perpendicular distance from the pivot (hinges)
- Pushing at the edge gives a larger perpendicular distance from the pivot (hinges), so a smaller force is needed to produce the same moment
- Pushing close to the hinges gives a very small perpendicular distance, so a much larger force is needed to produce the same moment
- If the force is doubled (with distance unchanged), the moment is doubled
Key terms in this question
Related
- All Eduqas GCSE Physics revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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