Ncert Exercises & Solutions

One day in the morning, Ramesh filled up 1/3 bucket of hot water from the geyser to take bath. The remaining 2/3 was to be filled with cold water (at room temperature) to bring the mixture to a comfortable temperature. Suddenly Ramesh had to attend to something which would take some time, say 5-10 min before he could take bath. Now, he had two options:
(i) Fill the remaining bucket completely with cold water and then attend to work.
(ii) First attend to the work and fill the remaining bucket just before taking bath. Which option do you think would have kept water warmer?
Explain.

Hint: Apply the concept of Newton's law of cooling.

STep 1: Find in which case, the rate of cooling is high or less.

The first option would have kept water warmer because according to Newton’s law of cooling, the rate of loss of heat is directly proportional to the difference of temperature of the body and the surrounding and in the first case, the temperature difference is less, so the rate of loss of heat will be less.

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