An object kept in a large room having an air temperature of 25^ takes 12 min to cool from 80^ to 70^ . The time taken to cool for the same object from - PHYSICS MCQ NEET 2019 2026 | ExamTest.live

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An object kept in a large room having an air temperature of 2 5^{\circ} C takes 12 min to cool from 8 0^{\circ} C to 7 0^{\circ} C . The time taken to cool for the same object from 7 0^{\circ} C to 6 0^{\circ} C would be nearly:

Solution & Step-by-step Explanation

According to Newton's Law of Cooling: \frac{T _{1} - T _{2}}{t} = K [\frac{T _{1} + T _{2}}{2} - T_{s}] .Case 1: \frac{80 - 70}{12} = K [\frac{80 + 70}{2} - 25] ⟹ \frac{10}{12} = K (75 - 25) = 50 K ⟹ K = \frac{1}{60} .Case 2: \frac{70 - 60}{t} = K [\frac{70 + 60}{2} - 25] ⟹ \frac{10}{t} = \frac{1}{60} (65 - 25) = \frac{40}{60} = \frac{2}{3} . \frac{10}{t} = \frac{2}{3} ⟹ t = 15 min .

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An object kept in a large room having an air temperature of 2 5^{\circ} C takes 12 min to cool from 8 0^{\circ} C to 7 0^{\circ} C . The time taken to cool for the same object from 7 0^{\circ} C to 6 0^{\circ} C would be nearly:

10 min

12 min

20 min

15 min

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