590 Heat and the First Law of ThermodynamicsP20.47P==×⋅×LNMOQP−σπAeT488245669610469009655800...Wm KmK24ejejafbg=×377 1026. WP20.48Suppose the pizza is 70 cm in diameter and A=20cm thick, sizzling at 100°C. It cannot lose heat byconduction or convection. It radiates according to =σAeT4. Here, Ais its surface area,Arr=+=+=2220 3520 350 020 8122ππππA..m mmm2af.Suppose it is dark in the infrared, with emissivity about 0.8. Then⋅=−567 10081080 37371010843.~mKWW2ejaf.If the density of the pizza is half that of water, its mass ismVr==ρρ225000 350 024Akg mmmkg3.Suppose its specific heat is c=⋅°06. cal g C. The drop in temperature of the pizza is described by:QmcT TdQdtmcdTdtdTdtmcfiff=−−⋅⋅°=°−dibg071040641860071JskgJ kg CCsKs..~P20.49=AeT42 005 67 100 250 100 9501 49 103 49 1086414143..W WmKmK K24⋅×=×−−ejafTTP20.50We suppose the earth below is an insulator. The square meter must radiate in the infrared as muchenergy as it absorbs,
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This note was uploaded on 12/14/2011 for the course PHY 203 taught by Professor Staff during the Fall '11 term at Indiana State University .