594_Physics ProblemsTechnical Physics

# 594_Physics ProblemsTechnical Physics - 596 P20.65 Heat and...

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596 Heat and the First Law of Thermodynamics P20.65 Energy goes in at a constant rate P . For the period from 50 0 10 0 10 4186 2 00 0 . .. min to 60.0 min, min kg J kg C C C Qm cT m i = =+ °° ° af bg b g 10 0 83 7 8 37 . min kJ kJ kg afbg m i (1) For the period from 0 to 50.0 min, L if = 50 0 3 33 10 5 min J kg a f ej m i Substitute = × m i 333 10 50 0 5 . . Jkg min into Equation (1) to find m m m i i i 500 83 7 8 37 83 7 837 144 5 . . . . . × = = kJ kJ kg kJ 66.6 kJ kg kg a f 0.00 1.00 2.00 3.00 20.0 40.0 60.0 T ( ° C) t (min) FIG. P20.65 P20.66 (a) The block starts with Km v ii == = 1 2 1 2 160 250 2 2 . kg m s J b g All this becomes extra internal energy in ice, melting some according to “ ” QmL f = ice . Thus, the mass of ice that melts is m Q L K L f i f ice 5 J 3.33 10 J kg kg mg = × = “” . 150 10
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