2025 · Paper 2 · Physics
Question 11
The printed question, the official key, and each model’s JSON answer plus the reasoning it wrote.
Q11
Official 1.6

Model answers
Claude Fable 5.1
Anthropic
1.6
Claude Fable 5.1 reasoning
**Setting up the cycle** From the V‑T diagram: - W → X: adiabatic (curve), volume increases 64 → 125 cm³ - X → Y: isobaric (straight line through origin, since V ∝ T at constant P), volume 125 → 250 cm³ - Y → Z: adiabatic - Z → W: isobaric **Step 1: Temperature at X (adiabatic W → X)** For a monatomic ideal gas, γ = 5/3, so TV^(γ−1) = TV^(2/3) = constant. T_X = T_W (V_W/V_X)^(2/3) = T_W (64/125)^(2/3) = T_W (4/5)² = (16/25) T_W **Step 2: Temperature at Y (isobaric X → Y)** At constant pressure, T ∝ V: T_Y = T_X (V_Y/V_X) = (16/25) T_W × 2 = (32/25) T_W **Step 3: Heat absorbed along XY** Q_XY = n C_p ΔT = (5/2) nR (T_Y − T_X) = (5/2) nR T_W (32/25 − 16/25) = (5/2)(16/25) nRT_W = (8/5)(1 J) = 1.6 J
GPT 6 Astra
OpenAI
1.6
GPT 6 Astra reasoning
No written reasoning was returned for this item.
GPT 5.6 Luna
OpenAI
1.6
GPT 5.6 Luna reasoning
No written reasoning was returned for this item.