physics
2007-10-30 2:18 am
Kelly prepares a cup of juice by mixing juice powder and some hot water. The juice has a mass of 0.3kg and is at 68℃. Find the minimum amount of ice at 0℃ that should be added to the juice in order to cool it to 15℃. Given c(juice) = 4000J/kg/℃)
回答 (2)
2007-10-30 2:43 am
✔ 最佳答案
Let the min mass of ice required be mkg and assume no enery lost to the surroundings during mixing. By E = ml, the energy required for the ice to melt completely:
E = ( 3.34 x 10^5 )m
Then by E = mc△T,
( 3.34 x 10^5 )m + m ( 4200 )( 15 - 0 ) = 0.3 ( 4000 )( 68 - 15 )
397000m = 63600
m = 0.160kg ( cor. to 3 s.f. )
So the mass of ice is 0.160kg.
參考: My Phy Knowledge
2007-10-30 2:44 am
Let m be the minimum amount of ice added to the juice
The energy of the juice gain = The energy of the ice loss
(0.3)(4000)(68 - 15) = m(334 000) + m(4200)(15 - 0)
63600 = 397000m
m = 0.160201511 kg
m = 0.16 kg
The energy of the juice gain = The energy of the ice loss
(0.3)(4000)(68 - 15) = m(334 000) + m(4200)(15 - 0)
63600 = 397000m
m = 0.160201511 kg
m = 0.16 kg
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