2025 · Paper 2 · Physics

Question 13

The printed question, the official key, and each model’s JSON answer plus the reasoning it wrote.

PhysicsPaper 2Numerical

Q13

Official 0.2

JEE Advanced 2025 Paper 2 Physics question 13, page 1JEE Advanced 2025 Paper 2 Physics question 13, page 2

Model answers

Claude Fable 5.1

Anthropic

Correct4 / 4

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

Correct4 / 4

0.2

GPT 6 Astra reasoning

No written reasoning was returned for this item.

GPT 5.6 Luna

OpenAI

Correct4 / 4

0.2

GPT 5.6 Luna reasoning

No written reasoning was returned for this item.