A liquid cools down from ${70^o}C$ to ${60^o}C$ in $5$ minutes. The time taken to cool it from ${60^o}C$ to ${50^o}C$ will be
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(c) According to Newton's law of cooling
Rate of cooling ? mean temperature difference.
Initially, mean temperature difference $ = \left( {\frac{{70 + 60}}{2} - {\theta _0}} \right) = (65 - {\theta _0})$
Finally, mean temperature difference $ = \left( {\frac{{60 + 50}}{2} - {\theta _0}} \right) = (55 - {\theta _0})$
In 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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