AQA AS Level Physics Paper 2, June 2024: Question 11

✅ Correct Answer: D

y = speed and Air resistance = not negligible

💡 Key Knowledge

• Shape of graph: The curve starts with a steep gradient (high acceleration) that gradually flattens out to a horizontal line (zero acceleration/constant value).
• Terminal Velocity: When an object falls, air resistance increases with speed until it balances the weight. Acceleration drops to zero, and the object reaches terminal velocity (represented by the flat top section).
• Why not distance?: If y were distance, a flattening graph would mean speed is dropping to zero (stopping mid-air), which is physically impossible for a freely falling object. Furthermore, distance-time graphs for falling objects curve upwards endlessly with an increasing gradient.

🧠 Exam Technique

When analyzing multiple-choice physics graphs, break them down into two distinct phases:

1. Check the gradient at t = 0 : It starts at zero (or steep depending on axes), but notice how the gradient represents the *rate of change* of y .
2. Check the final state: A flat horizontal line on a speed-time graph means constant speed (terminal velocity). On a distance-time graph, a flat line means the object has stopped moving completely.

❌ Common Errors

• Confusing graph types: Many students automatically associate "curves flattening out" with distance or displacement, forgetting that displacement-time graphs curve upwards (steeper gradient) as an object speeds up under gravity.
• Assuming negligible air resistance: If air resistance were negligible, the object would continue to accelerate indefinitely at g = 9.81 m s⁻² , resulting in a straight line with a constant, non-zero gradient on a speed-time graph. The flattening curve proves air resistance is significant.