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A body takes 10 minutes to cool from 60°C to 50°C. The temperature of surroundings is constant at 25°C. Then, the temperature of the body after next 10 minutes will be approximately-

1. 43°C
2. 47°C
3. 41°C
4. 45°C

Correct answer: 43°C

Solution

Using (T1-T2)/t = k[(T1+T2)/2 - T0]: first interval gives 1 = k(55-25) so k = 1/30. Next interval: (50-T)/10 = (1/30)((50+T)/2 - 25) = T/60, giving 6(50-T) = T, so T = 300/7 ≈ 43°C.

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