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Newton's law of cooling: time taken to cool to a given temperature

The same question, asked 3 times: 23 Apr 2025 S1*, 13 Apr 2026 S2*, 18 Apr 2026 S1. Every wording below, oldest first.

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  1. Question 1

    23 Apr 2025 S1

    114
    The rate at which a substance cools in moving air, is proportional to the difference between the temperature of the substance and that of air. The temperature of air is 290 K and the substance cools from 370 K to 330 K in 10 minutes. Then the time to cool the substance up to 295 K is

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  2. Question 2

    13 Apr 2026 S2

    87
    A body cools according to Newton's law of cooling from 100∘100^\circC to 60∘60^\circC in 2020 minutes. The temperature of the surroundings being 20∘20^\circC, then the total time required for the body to cool down to 30∘30^\circC is

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  3. Question 3

    18 Apr 2026 S1

    86
    A body cools from 100 ∘C100\ ^\circ\mathrm{C} to 60 ∘C60\ ^\circ\mathrm{C} in 20 minutes, the temperature of the surroundings being 20 ∘C20\ ^\circ\mathrm{C}. The total time taken (in minutes) for the body to cool down to 40 ∘C40\ ^\circ\mathrm{C} is ...

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