MYP Physics · 08 · extended response
Reserve buoyancy for a rescue platform
Pressure and fluids · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- discriminating
- Marks
- 8
- Topics
- 2
- Answer
- Complete
A sealed rescue platform has external volume 0.60 m³ and mass 120 kg. It operates in fresh water of density 1000 kg m⁻³. Designers require no more than 80% of its volume to be submerged in calm water, leaving reserve buoyancy. Each person is represented by a mass of 65 kg.
- a
Determine Determine the maximum total supported mass at the 80% submergence limit.
3 marks - b
Calculate Calculate the maximum whole number of represented people that can board without exceeding the design limit.
2 marks - c
Evaluate Evaluate whether advertising a five-person capacity is justified from this calculation alone.
3 marks
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a
Determine Determine the maximum total supported mass at the 80% submergence limit.
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 displaced volume at the limit = 0.80 × 0.60 = 0.48 m³.
- 2
Uses floating equilibrium so supported mass equals displaced-water mass.
- 3
Obtains maximum total mass = 1000 × 0.48 = 480 kg.
b
Calculate Calculate the maximum whole number of represented people that can board without exceeding the design limit.
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
Finds available payload mass = 480 − 120 = 360 kg.
- 2
Calculates 360 ÷ 65 = 5.54 and therefore limits the platform to 5 whole people under this model.
c
Evaluate Evaluate whether advertising a five-person capacity is justified from this calculation alone.
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
Recognises that the calculation uses a simplified fixed person mass and calm fresh water.
- 2
Identifies a relevant real condition such as equipment mass, waves, uneven loading, leakage, dynamic boarding, or water density.
- 3
Recommends safety-factor testing or a lower rated capacity until stability and worst-case loading are verified.
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