In Joule's experiment, an insulated container contains 20 kg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighing 40 kg through a height of 4 m. The process is repeated 500 times. The acceleration due to gravity is 9.8 ms-2. Neglecting the heat capacity of agitator, the temperature of water (in °C) is________________?
Correct answer: B. 34.4
- A. 40.5
- B. 34.4
- C. 26.8
- D. 25
Explanation
The stirring work is 40 × 9.8 × 4 × 500 = 784 kJ, which raises 20 kg of water by about 784/(20 × 4.18) = 9.4°C. Adding this rise to 25°C gives approximately 34.4°C.
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