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Bài 3 (3 điểm). Một người thả 450g sắt ở nhiệt độ 100°C vào 500g nước ở nhiệt độ 50°C làm cho nước nóng lên tới 54,5°C. Cho nhiệt dung riêng của nước là 4200 J/kg.K và bỏ qua sự hao phi nhiệt ra mỗi trường bên ngoài. Hãy tính: a. Nhiệt độ của sắt khi có sự cân bằng nhiệt. b. Nhiệt dung riêng của sắt. c. Nếu muốn nước và sắt nóng tới nhiệt 70°C thi cần thêm bạo nhiêu kg sắt ở nhiệt độ 150°C.
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