2025 · Paper 2 · Physics
Question 13
The printed question, the official key, and each model’s JSON answer plus the reasoning it wrote.
Q13
Official 0.2


Model answers
Claude Fable 5.1
Anthropic
0.2
Claude Fable 5.1 reasoning
Thermal equilibrium: same temperature T on both sides (piston conducting). Volumes equal (L/2 each). Left pressure: P_L = (3/2)RT/(AL/2) = 3RT/(AL) Right pressure: P_R = RT/(AL/2) = 2RT/(AL) So P_L = (3/2)P_R. Spring natural length 2L/5, compressed to L/2, so compression x = L/2 − 2L/5 = L/10. Spring is compressed and pushes the piston to the right with force kL/10. Piston equilibrium: P_L A + kL/10 = P_R A → (3/2)P_R A + kL/10 = P_R A → P_R A = −kL/5 Sign issue: spring compressed pushes rightward, left pressure larger also pushes right — inconsistent. So the spring must be stretched (attached at left wall, natural length 2L/5, current length L/2 means stretched by L/10, pulling the piston leftward): P_L A = P_R A + kL/10 → (1/2)P_R A = kL/10 → P_R = kL/(5A) α = 0.2
GPT 6 Astra
OpenAI
0.2
GPT 6 Astra reasoning
No written reasoning was returned for this item.
GPT 5.6 Luna
OpenAI
0.2
GPT 5.6 Luna reasoning
No written reasoning was returned for this item.