Practice question
Question
A 0.2kg aluminium block at 120∘C is placed in 0.8kg of water at 20∘C in a 0.1kg copper calorimeter at 20∘C. What is the final temperature? (Specific heat of aluminium = 900J kg−1K−1, water = 4186J kg−1K−1, copper = 386Jkg−1K−1)
Explanation
Heat lost = Heat gained. 0.2×900×(120−T) = (0.8×4186+0.1×386)×(T−20). 21600−180T = (3348.8+38.6)×(T−20) = 3387.4T−67748. 21600+67748 = 3387.4T+180T. 89348 = 3567.4T⇒T≈25.04∘C≈25∘C. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 25°C. This satisfies dimensional consistency and physical conditions given, so option A is scientifically correct.
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