Determine the mass of the cast iron sample if 81 kJ of heat was spent on heating it from 50 to 75 s, note that the total heat loss was 60 percent
Given: t0 (initial temperature of the cast iron sample) = 50 ºС; t (final temperature) = 75 ºС; Qz (spent heat) = 81 kJ (81 * 103 J); η (process efficiency) = 40% (heat loss is 60%).
Constants: Cch (specific heat capacity of cast iron) = 540 J / (kg * K).
We express the mass of the cast iron sample from the formula: η = Qp / Qz = M * m * (t – t0) / Qz, whence m = Qz * η / (M * (t – t0)).
Let’s calculate: m = 81 * 103 * 0.4 / (540 * (75 – 50)) = 2.4 kg.
Answer: The mass of the cast iron sample taken is 2.4 kg.
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