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

According to Newton's law of cooling,Rate of cooling ∞ mean temperature differenceInitially, mean temperature difference=70+602−θ0=65−θ0Finally, mean temperature difference=60+502−θ0=55−θ0In second case, mean temperature difference decreases, so rate of fall of temperature decreases. Thus, it takes more time to cool through the same range.