AQA AS Level Physics Paper 2, June 2024: Question 20

✅ Correct Answer: C

proportional to t.

Since velocity increases linearly with time in free fall ($v = u + at$), and momentum is directly proportional to velocity ($p = mv$), momentum must also increase linearly, making it directly proportional to time $t$.

💡 Key Knowledge

• Momentum definition: p = mv (where m is mass and v is velocity).
• SUVAT equations: For an object falling from rest ( u = 0 ) with negligible air resistance, acceleration is constant ($a = g$). Therefore, v = gt .
• Combining equations: Substituting v = gt into p = mv yields p = mgt . Since mass ($m$) and acceleration due to gravity ($g$) are constant, p is directly proportional to t .

🧠 Exam Technique

For multiple-choice questions involving proportionalities, write down the fundamental physics equations linking the variables before looking at the options. Do not confuse displacement (which depends on t² ) with velocity or momentum (which depend linearly on t ).

❌ Common Errors

• Choosing D (proportional to t²) by confusing momentum with displacement ( s = ½gt² ).
• Choosing B (proportional to √t) by mixing up acceleration formulas with root-time relationships.
• Choosing A (constant) by forgetting that velocity increases as an object falls under gravity.