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A 5 g piece of ice at -20 deg C is dropped into 10 g of water at 30 deg C. Assuming heat is exchanged only between the ice and the water, find the final temperature of the mixture. (Specific heat of ice = 2100 J/kg/deg C, specific heat of water = 4200 J/kg/deg C, latent heat of fusion = 3.36e5 J/kg.)

1. -5 deg C
2. 0 deg C
3. 5 deg C
4. 10 deg C

Correct answer: 0 deg C

Solution

Water cooling to 0 deg C releases 1260 J; warming the ice to 0 deg C uses 210 J, leaving 1050 J, which melts only part of the ice (full melt needs 1680 J), so the final temperature is 0 deg C.

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