question_answer 43)

                  One day in the morning, Ramesh filled up 1/3 bucket of hot water from geyser, to take bath. Remaining 2/3 was to be filled by cold water (at room temperature) to bring mixture to a comfortable temperature. Suddenly Ramesh had to attend to something which would take some time, say 5-10 minutes before he could take bath. Now he had two options: (i) fill the remaining bucket completely by cold water and then attend to the 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.                

Answer:

                  First option would keep water warmer. According to Newton's law of cooling, rate of loss of heat by a body is directly proportional to the temperature difference between the body and its surrounding. If temperature difference is small, the rate of loss of beat by water will be small and hence it remains warmer for long time.