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Question
A bucket contains 10 liters of water at 80°C. Cold water at 25°C is run from a tap into the bucket of hot water for 20 seconds and the temp. Of the water in the bucket falls to 50°C.
(a) Calculate the rate at which cold water came out of the tap.
(b) State an assumption made in the above calculation.
Solution
(a) Mass of water in the bucket = Density x Volume
= 1000 kg/m3 x 0.01 m3 = 10 kg
Let the mass of water chat came out from the tap be m.
Heat lost by hot water = Heat gained by cold water
10 x 4200 x (80 - 50) = m x 4200 x (50 - 25)
300 = 25m
m=12 kg
12 kg of water came out of tap in 20 sec.
So, the rate at which cold water came out of the tap is `12/20` = 0.6 kg/s = 600 g /s
(b) In the above calculation we assumed chat there is no loss of heat to the surroundings
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