Q34. A liquid cools down from 70°C to 60°C in 5 minutes. The time taken to cool it from 60°C to 50°C will be (1) 5 minutes
(2) Lesser than 5 minutes
(3) Greater than 5 minutes
(4) Lesser or greater than 5 minutes depending upon the density of the liquid​

According to Newton's law of cooling ,

Rate of cooling ∝ Mean temperature difference.

Initially, mean temperature difference =(

2

70+60

−θ

0

)=(65−θ

0

)

Finally, mean temperature difference =(

2

60+50

−θ

0

)=(55−θ

0

)

In the second case , mean temperature difference decreases, so rate of fall of temperature decreases, so it takes more time to cool through the same range.

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