AQA A-Level Physics Paper 1, June 2023: Question 22
1 mark · Medium difficulty · Multiple Choice
Identify the direction of the reaction force of the hinge on a heavy uniform trapdoor held open by a rope.
Practise this questionQuestion
Question text
22 A heavy uniform trapdoor is hinged to the floor. It is held open by a rope as shown.
Which arrow shows the direction of the reaction force of the hinge on the trapdoor?
[1 mark]
A
B
C
D
Mark scheme
Show the mark scheme
22 B B
How to answer it
Trapdoor Hinge Reaction Force
This question assesses your understanding of static equilibrium, the principle of moments, and the graphical determination of concurrent forces acting on an extended rigid body.
Question Part 2.2
Identifying the direction of the reaction force at the hinge
✅ Correct Answer
B
💡 Key Knowledge
- Condition for Equilibrium: For an object in translational and rotational equilibrium, the lines of action of all coplanar forces acting on the object must pass through a single common point (concurrent forces) if there are only three forces, OR the vector sum of forces and sum of moments must both equal zero.
- Forces acting on the trapdoor: 1. Weight acting downwards through the center of mass.
2. Tension in the rope pulling upwards and to the left.
3. Reaction force from the hinge acting on the trapdoor.
🧠 Exam Technique
Extend the line of action of the weight (acting vertically downwards from the middle of the trapdoor) and the line of action of the tension in the rope. Follow these two lines until they intersect. For the trapdoor to remain in equilibrium, the line of action of the hinge's reaction force must also pass through this exact intersection point. Arrow B is the only option pointing directly toward that convergence point.
❌ Common Errors
- Assuming the reaction force always acts straight up or directly along the length of the trapdoor.
- Failing to consider the principle of concurrent forces for three-force equilibria, leading to random guessing between diagonal arrows.
Topics
Physics · 3.4 Mechanics and materials
Question and mark scheme from the AQA A-Level Physics examination, Paper 1, June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.