AQA GCSE Physics Physics Paper 2 (Foundation), June 2025: Question 9

✅ Correct Answers [1 Mark]

• Force (applied to spring)
• Weight (of the masses)
• Also allowed: Mass (hung from spring)

🧠 Exam Technique

Remember the golden rule:

• Independent variable: The thing you choose to change (the weight/force added).
• Dependent variable: The thing that is measured as a result (length or extension of the spring).

✅ Acceptable Pairs [2 Marks]

Option 1:

• Risk: Stand could topple over and hit / injure student [1 mark]
• Precaution: Clamp the base of the stand to the desk with a G-clamp (or place heavy masses on the base) [1 mark]

Option 2:

• Risk: Masses could slip off and fall onto feet / toes [1 mark]
• Precaution: Work standing up (step back) / clamp base / limit mass used [1 mark]

Option 3:

• Risk: Spring snaps / recoils and hits eyes / face [1 mark]
• Precaution: Wear safety goggles [1 mark]

❌ Common Errors

• Incomplete risk: Writing just "stand falls" or "spring snaps" without stating how it causes harm (e.g., must say "and hurts/hits student").
• Unmatched precautions: Pairing "weights falling on feet" with "wear goggles". The precaution must specifically reduce the stated risk!

✅ Any Two Improvements [2 Marks]

• Clamp the ruler upright (close to the spring) rather than holding it by hand.
• Ensure the ruler is vertical (e.g. using a set square or plumb line).
• Attach a pointer / fiducial marker (e.g. a horizontal splint) to the bottom of the spring.
• Use a ruler with higher resolution (e.g. millimetre markings).
• Also allowed: Move ruler so it is directly aligned with the spring to prevent parallax error.

🧠 Exam Technique: Look at the Diagram

Figure 13 shows a student's hand physically holding a wobbly wooden ruler tilted away from the spring! This instantly tells you what needs fixing:

• Holding by hand causes wobbling and angle errors → Clamp it!
• Gap between ruler and spring creates parallax errors → Add a pointer / move closer!

✅ Correct Answer [1 Mark]

• The unstretched / initial length of the spring is not zero (it is approximately 3.0 cm at 0 N).
• OR: The student plotted length on the y-axis, not extension.
• OR: The spring length is not directly proportional to force.

💡 Key Knowledge: Length vs. Extension

• Extension = New Length − Original Length
• Force ∝ Extension: An extension–force graph is a straight line through the origin (0, 0).
• Length–force graph: The y-intercept represents the original unweighted length of the spring ( L₀ ≈ 3.0 cm ).

✅ Correct Answer [2 Marks]

• The spring has exceeded its limit of proportionality (or no longer obeys Hooke's Law) [1 mark]
• The spring is inelastically (plastically) deformed [1 mark]
• OR: The extension is no longer directly proportional to the force applied [1 mark]

❌ Common Errors

• Confusing elastic and inelastic: Calling it "elastically deformed" gets 0 marks for that point.
• Vague descriptions like "the spring gets stretched too much" or "it gets tired". Always use precise physics vocabulary: limit of proportionality and inelastic deformation.

✅ Correct Selection [1 Mark]

☑ force = spring constant × extension

💡 Symbol Equation

F = k × e

• F = Force in Newtons (N)
• k = Spring constant in Newtons per metre (N/m)
• e = Extension in metres (m)

📐 Step-by-Step Calculation

Given values:

• Force, F = 4.0 N
• Extension, e = 0.064 m

Step 1: Substitute into the formula [1 Mark]

4.0 = k × 0.064

Step 2: Rearrange for k [1 Mark]

k = 4.0 / 0.064

Step 3: Calculate the final answer [1 Mark]

k = 62.5 N/m

❌ Common Calculation Traps

• Inversion error: Calculating 0.064 / 4.0 = 0.016 (dividing extension by force). Always write the substitution step first to avoid flipping terms!
• Unit checks: Here, the extension was already given in metres ( 0.064 m ). If it were given in centimetres (e.g. 6.4 cm), you would need to divide by 100 first.