2025 · Paper 1 · Physics
Question 2
The printed question, the official key, and each model’s JSON answer plus the reasoning it wrote.
Q02
Official D

Model answers
Claude Fable 5.1
Anthropic
D
Claude Fable 5.1 reasoning
Maximum scattering angle of a heavier projectile (mass M) off a lighter target (mass m) at rest in an elastic collision: sin θ_max = m/M. Here M = 2m, so sin θ_max = 1/2 → θ_max = π/6. **Derivation sketch:** In the CM frame, the heavy particle's speed is v_cm-relative = m·u/(2m+m) = u/3, and the CM velocity is 2mu/(3m) = 2u/3. The lab velocity of the heavy particle is the vector sum of the CM velocity (2u/3) and a vector of magnitude u/3 in any direction; the maximum deflection occurs when this is tangent, giving sin θ_max = (u/3)/(2u/3) = 1/2, so θ_max = π/6.
GPT 6 Astra
OpenAI
D
GPT 6 Astra reasoning
No written reasoning was returned for this item.
GPT 5.6 Luna
OpenAI
D
GPT 5.6 Luna reasoning
No written reasoning was returned for this item.