588_Physics ProblemsTechnical Physics

588_Physics ProblemsTechnical Physics - 590 P20.47 Heat and...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
590 Heat and the First Law of Thermodynamics P20.47 P == × × L N M O Q P σπ AeT 48 8 2 4 5 6 6 9 61 0 46 9 0 0 9 6 55 8 0 0 .. . Wm K m K 24 ej e j a f bg 377 10 26 . W P20.48 Suppose the pizza is 70 cm in diameter and A = 20 cm thick, sizzling at 100°C. It cannot lose heat by conduction or convection. It radiates according to = σ AeT 4 . Here, A is its surface area, Ar r =+= + = 2 2 2 0 35 2 0 35 0 02 0 81 2 2 πππ π A . . m m m m 2 af . Suppose it is dark in the infrared, with emissivity about 0.8. Then = 567 10 081 080 373 710 10 8 4 3 . ~ m K W W 2 e j a f . If the density of the pizza is half that of water, its mass is mV r = = ρρ 2 2 500 0 35 0 02 4 A kg m m m kg 3 . Suppose its specific heat is c =⋅ ° 06 . cal g C. The drop in temperature of the pizza is described by: Qm c T T dQ dt mc dT dt dT dt mc fi f f =− ⋅⋅ ° di b g 0 710 40 6 4 1 8 6 007 1 Js kg J kg C Cs Ks . .~ P20.49 = AeT 4 2 00 5 67 10 0 250 10 0 950 1 49 10 3 49 10 86 4 14 14 3 . . W W m K m K K 2 4 × = × −− e j a f T T P20.50 We suppose the earth below is an insulator. The square meter must radiate in the infrared as much energy as it absorbs,
Background image of page 1
This is the end of the preview. Sign up to access the rest of the document.

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 .

Ask a homework question - tutors are online