# Physics Module 2 HelpWatch

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#1
A container holding 2.3 litres of milk at 15 degree's C is put into a freezer. Calculate the energy that must be removed from the milk tor eduece its temperature to the freezer temperature of -30 degrees C. Assume that milk behaves like water and ice.

SHC of water = 4.2
SHC of ice = 2.1
Specific latent heat of fusion = 330
density of water = 1kg litre-1

Gotto work out energy removed [6 marks]
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#2
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14 years ago
#3
(Original post by nas7232)
A container holding 2.3 litres of milk at 15 degree's C is put into a freezer. Calculate the energy that must be removed from the milk tor eduece its temperature to the freezer temperature of -30 degrees C. Assume that milk behaves like water and ice.

SHC of water = 4.2
SHC of ice = 2.1
Specific latent heat of fusion = 330
density of water = 1kg litre-1

Gotto work out energy removed [6 marks]
I think it will be (2.3 x 4.2 x 15) + (330 x 2.3) + (2.3 x 2.1 x 30) KJ
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#4
wouldn't it be

H=mc T H = Lm + H=mc T
((2.3 litre x 1kg litre-1) x 4.2 x 15) + (330 x 2.3) + (2.3 x 2.1 x 30) KJ

What happeerend to the delta T in the last two bits

Also the last bit asks for:

It costs 8.2p per KWh to remove energy from the freezer. what is the cost of freezing the milk
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14 years ago
#5
you will have to reduce the milk to 0 *C

then you wil have to freeze it

then you will have to reduce the ice to -30 *C

mass of the milk/ice = 2.3 kg

=> E = (2.3 * 4.2 * 15) + (2.3 * 330) + (2.3 * 2.1 * 30) = 1048.8 KJ

1 kWh = 1000 * 60 * 60 = 3600 KJ

=> price = 1048.8/3600 = 29p
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#6
Thanks
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