Answer: 33.3°C.
- A 40°C
- B 33.3°C
- C 46.6°C
- D 50°C
Correct answer: B. 33.3°C
Explanation: Heat lost by A = heat gained by B: m×2000×(80-T) = m×4000×(T-20). Solving: 2000(80-T)=4000(T-20) → 160000-2000T=4000T-80000 → 240000=6000T → T=40°C. Correct equilibrium temperature is 40°C.
During a phase change (melting or boiling), temperature stays constant while heat is absorbed entirely as latent heat (Q=mL); temperature only rises again once the substance is fully in its new phase.
Concept context
Temperature scales, thermal expansion, calorimetry, and the three modes of heat transfer including radiation laws.