Practice question
Question
A 0.5kg silver block at 240∘C is placed in 1.5kg water at 21∘C in a 0.25kg copper calorimeter at 21∘C. What is the final temperature? (Specific heat of silver = 236J kg−1K−1, water = 4186J kg−1K−1, copper = 386J kg−1K−1)
Explanation
0.5×236×(240−T) = (1.5×4186+0.25×386)×(T−21). 28320−118T = (6279+96.5)×(T−21) = 6375.5T−133885.5. 28320+133885.5 = 6375.5T+118T. 162205.5 = 6493.5T⇒T≈24.97∘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 B is scientifically correct.