📘 Chapter 4: Turning Effect of Forces – Constructed Response Questions
Prepared by Muhammad Tayyab, Subject Specialist Physics, Govt Christian High School Daska. Based on PECTAA 2026 syllabus (National Curriculum 2023).
📖 What's Inside: This section covers constructed response questions from Chapter 4 Turning Effect of Forces including centripetal force relationship with radius, equilibrium and toppling, stability and centre of gravity, accelerated bodies and equilibrium, and effect of centre of gravity on stability. Each question is presented with a detailed answer as per the official PECTAA 2026 Physics curriculum. Perfect for Punjab Boards (Lahore, Gujranwala, Multan, etc.) and all BISE boards across Pakistan.
📚 Related Resources – Chapter 4: Turning Effect of Forces
📋 Exercise Short Qs
📝 Short Qs
📖 Comprehensive Qs
🔢 Numerical Problems
✅ MCQs
✏️ Constructed Response
Turning Effect of Forces covers torque, equilibrium, center of mass, and couple.
📖 Constructed Response Questions & Answers (PECTAA 2026)
4.1 A car travels at the same speed around two curves with different radii. For which radius the car experiences more centripetal force? Prove your answer.
Answer:
The car experiences more centripetal force when it travels around the curve with a smaller radius.
Proof:
\(F_c = \frac{mv^2}{r}\)
For the same mass \(m\) and speed \(v\), centripetal force \(F_c\) is inversely proportional to the radius \(r\). Therefore, a smaller radius means a greater centripetal force.
✅ Smaller radius → greater centripetal force (\(F_c \propto 1/r\)).
4.2 A ripe mango does not normally fall from the tree. But when the branch of the tree is shaken, the mango falls down easily. Can you tell the reason?
Answer:
When the branch is shaken, the mango is disturbed from its equilibrium position. If the centre of mass no longer remains above the base of support, the body tends to move further away from its original position and topples over.
✅ Shaking disturbs equilibrium; centre of mass moves outside base, causing toppling.
4.3 Discuss the concepts of stability and centre of gravity in relation to objects toppling over. Provide an example where an object's centre of gravity affects its stability, and explain how altering its base of support can influence stability.
Answer:
An object is more stable when its centre of gravity is low and its centre of mass lies within its base.
Example: A bus is more stable when its heavy loads are placed on the floor, lowering its centre of gravity.
Improving Stability: Stability can be improved by:
1. Lowering the centre of gravity.
2. Widening the base of support.
✅ Low CG and wide base → greater stability.
4.4 Why an accelerated body cannot be considered in equilibrium?
Answer:
A body is said to be in equilibrium if it has no acceleration. Therefore, an accelerated body cannot be considered in equilibrium.
✅ Equilibrium requires zero acceleration.
4.5 Two boxes of the same weight but different heights are lying on the floor of a truck. If the truck makes a sudden stop, which box is more likely to tumble over? Why?
Answer:
The taller box is more likely to tumble over because it has a higher centre of gravity.
A lower centre of gravity makes an object more stable, while raising the centre of gravity makes it less stable.
✅ Taller box (higher CG) is less stable and more likely to topple.
📐 Key Concepts – Turning Effect of Forces (Constructed Response)
Centripetal Force: \(F_c = \frac{mv^2}{r}\)
Equilibrium: No acceleration (\(\sum F = 0\), \(\sum \tau = 0\))
Stability: Low centre of gravity and wide base.
Toppling: Occurs when centre of gravity moves outside base of support.
💡 Exam Tip:
For constructed response questions, provide clear, well-structured answers with explanations and examples. These questions test your ability to apply concepts to real-world situations. Use the given space effectively to demonstrate your understanding. These questions follow the PECTAA 2026 pattern and are prepared by Subject Specialist Muhammad Tayyab.
Chapter 1Physical Quantities and Measurements
Chapter 2Kinematics
Chapter 3Dynamics
Chapter 4✨ Turning Effect of Forces
Chapter 5Work and Energy
Chapter 6Mechanical Properties of Matter
Chapter 7Thermal Properties of Matter
Chapter 8Magnetism
Chapter 9Nature of Science
📖 Complete syllabus coverage for Class 9 Physics (PECTAA 2026) – Chapters 1 to 9
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus