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578_Physics ProblemsTechnical Physics

# 578_Physics ProblemsTechnical Physics - 580*P20.6 Heat and...

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580 Heat and the First Law of Thermodynamics *P20.6 The laser energy output: P t × = × 1 60 10 4 00 10 13 9 4 .. J s 2.50 10 s J ej . The teakettle input: Qm cT == ° ° = × 0800 268 10 5 kg 4 186 J kg C 80 C J bg . This is larger by 6.70 times. P20.7 QQ cold hot =− mc T mc T TT T ff f ∆∆ af di b g water iron kg J kg C C kg J kg C C C ⋅° ° = − ⋅° ° 20 0 4186 25 0 1 50 448 600 29 6 . . P20.8 Let us find the energy transferred in one minute. Qmc m c T Q =+ =⋅ ° + ° ° = cup cup water water kg J kg C kg J kg C C J 0 200 900 0 800 1 50 5 290 . b g b g If this much energy is removed from the system each minute, the rate of removal is = = Q t 5290 88 2 88 2 J 60.0 s Js W . P20.9 (a) cold hot m c m cTT mcTT mc TT w w c c f c f unk unk
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