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EthF

2009-03-27 12:04 am

The initial temperature of a jar of juice is 80 ℃ and the mass of the juice is 2kg.Susan adds ice cubes into the jar in order to cool down the juice to 20 ℃.What is the minimum number of ice cubes at 0 ℃ required?

Given : Mass of each ice cube =0.15 kg
Specific heat capacity of juice =4700J/kg/ ℃
Specific heat capacity o water = 4200J/kg/℃
Specific latent heat of fusion of ice = 3.34 x 10^5

ANS:
A.8
B.9
C.10
D.11

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更新1:

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回答 (1)

Prof. Physics

2009-03-27 12:18 am

✔ 最佳答案

Energy lost by the juice

= mc(Tf - Ti)

= (2)(4700)(80 - 20)

= 564 000 J

For minimum number of ice cubes required, the ice should be turned to 20*C water finally.

Energy gained by the ices cube

= mlv + mc'T

= m(3.34 X 105 + 4200 X 20)

= 418 000m

Assume there is no heat lost to the surroundings,

heat gained by the ice = heat lost by the juice

418 000m = 564 000

m = 1.349 kg

So, the number of ice cubes required

= 1.349 / 0.15

= 8.995

= 9

The answer is B.

參考: Physics king

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