Practice question
Question
A 0.15kg mercury block at 400∘C is placed in 0.5kg water at 20∘C in a 0.05kg aluminium calorimeter at 20∘C. Find the final temperature. (Specific heat of mercury = 140J kg−1K−1, water = 4186J kg−1K−1, aluminium = 900Jkg−1K−1)
Explanation
0.15×140×(400−T) = (0.5×4186+0.05×900)×(T−20). 8400−21T = (2093+45)×(T−20) = 2138T−42760. 8400+42760 = 2138T+21T. 51160 = 2159T⇒T≈23.7∘C. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 23.7°C. This satisfies dimensional consistency and physical conditions given, so option D is scientifically correct.
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