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A calorimeter holding 50 g of water at 50 C cools to 45 C in 10 minutes. With 100 g of water at 50 C, the same cooling to 45 C takes 18 minutes. Find the water equivalent of the calorimeter.

1. 12.5 g
2. 15.0 g
3. 17.5 g
4. 20.0 g

Correct answer: 12.5 g

Solution

Equal heat-loss rate gives (50 + w)/10 = (100 + w)/18; solving, w = 12.5 g.

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