HW-H

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Unformatted text preview: 4 kg, Cliq=3000 J/kg K (heat capacity of the liquid) dQ dT = mCliq dt dt Since T changes linearly with time t, dQ = const . dt dQ 270 − 300 = 0.4 × 3000 × = −900 J / min dt 40 or 1. The latent heat LF, mLF = 30min x 900 J/min, or LF = 6.75 x 104 J/kg = 67.5 kJ/kg 2. The heat capacity Csol of the frozen phase dQ dT = mCsol dt dt or − 900 = 0.4Csol 250 − 270 = −0.4Csol 20 or Csol = 2250 J/kg K ((WileyPlus)) 34. While the sample is in its liquid phase, its temperature change (in absolute values) is | ∆ T | = 30 °C. Thus, with m = 0.40 kg, the absolute value of Eq. 18-14 leads to ° |Q| = c m |∆ T | = ( 3000 J/ kg × C )(0.40 kg)(30 °C ) = 36000 J . The rate (which is constant) is P = |Q| / t = (36000 J)/(40 min) = 900 J/min, which is equivalent to 15 Watts. (a) During the next 30 minutes, a phase change occurs which is described by Eq. 18-16: |Q| = P t = (900 J/min)(30 min) = 27000 J = L m . Thus, with m = 0.40 kg, we find L = 67500 J/kg ≈ 68 kJ/kg. (b) During the final 20 minutes, the sample is solid and undergoes a temperature change (in absolu...
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This note was uploaded on 05/14/2013 for the course MATH 346 taught by Professor Professormiguelarcones during the Spring '08 term at Binghamton University.

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