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NDA 2020 GAT · General Knowledge · Heat and Thermal Physics · easy

When 1 kg of water at 80 degrees C is mixed with 1 kg of water at 20 degrees C in an insulated container, the final temperature is

Single correct option

When 1 kg of water at 80 degrees C is mixed with 1 kg of water at 20 degrees C in an insulated container, the final temperature is
  1. A. 60 degrees C
  2. B. 40 degrees C
  3. C. 100 degrees C
  4. D. 50 degrees C
Show answer and solution

Answer: (D) 50 degrees C

Heat lost by hot water equals heat gained by cold water. Since masses and specific heats are equal, m c (80 - T) = m c (T - 20), giving T = 50 degrees C, the simple mean. The temperatures do not add up, so 100 is impossible, and unequal masses would shift the result.
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Original question written in the NDA 2020 GAT pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake