MYP Physics · 06 · extended response
Material choice for a bicycle rack
Matter, density, and materials · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- discriminating
- Marks
- 8
- Topics
- 2
- Answer
- Complete
A designer is choosing a material for a bicycle luggage rack. The rack must be light, safely support repeated loads, resist outdoor use, and be affordable.
| Material | Density / g cm⁻³ | Yield strength / MPa | Recycled content / % | Relative cost |
|---|---|---|---|---|
| Aluminium alloy | 2.7 | 240 | 55 | 2.0 |
| Mild steel | 7.8 | 260 | 70 | 1.0 |
| Magnesium alloy | 1.8 | 190 | 20 | 3.1 |
- a
Compare Calculate yield strength divided by density for each material and use it as one measure of strength for mass.
3 marks - b
Recommend Recommend a material using at least three pieces of evidence and a clear priority.
3 marks - c
Evaluate Identify one important limitation of this table and state what should be tested next.
2 marks
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a
Compare Calculate yield strength divided by density for each material and use it as one measure of strength for mass.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Calculates aluminium alloy: 240 ÷ 2.7 ≈ 89 in consistent comparative units.
- 2
Calculates mild steel: 260 ÷ 7.8 ≈ 33 and magnesium alloy: 190 ÷ 1.8 ≈ 106.
- 3
Identifies magnesium alloy as having the greatest value by this single measure.
b
Recommend Recommend a material using at least three pieces of evidence and a clear priority.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Makes a defensible recommendation consistent with a stated design priority.
- 2
Uses at least three accurate comparisons from density, strength, recycled content, and cost.
- 3
Recognises a trade-off rather than claiming that one row is universally best.
c
Evaluate Identify one important limitation of this table and state what should be tested next.
Build a chain of claim, evidence and physics reasoning. Address more than one relevant factor, identify a limitation or assumption, and finish with a conclusion that is conditional on the evidence rather than absolute.
- 1
Identifies missing evidence relevant to repeated outdoor use, such as fatigue life, corrosion resistance, joint strength, or coating requirements.
- 2
Proposes a corresponding controlled durability, corrosion, or loaded-cycle test.
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