A body cools in 7 minutes from 60° C to 40° C. What time (in minutes) does it take to cool from 40° C to 28° C, if its surrounding temperature is 10° C? (Newton's law of cooling holds good) (a) 3.5 (b) 10 (c) 11 (d) 7

Answer: (d). Newton's law: (T₁ - T₂)/(t) = k((T₁ + T₂)/(2) - T₀). Case 1: 20/7 = k(50 - 10) = 40k ⇒ k = 1/14 Case 2: 12/t = 1/14(34 - 10) = 24/14 t = 7 min So the answer is (d) 7.

A body cools in 7 minutes from 60° C to 40° C. What time (in minutes)… | MHT CET 2026 (11 Apr, Shift 2)

Q5MHT CET 2026 · 11 APR · SHIFT 2Medium

Newton's Law of Cooling

A body cools in $7$ minutes from $60^\circ$ C to $40^\circ$ C. What time (in minutes) does it take to cool from $40^\circ$ C to $28^\circ$ C, if its surrounding temperature is $10^\circ$ C? (Newton's law of cooling holds good)

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Answer: (d)

Newton's law: $\frac{T_1 - T_2}{t} = k\left(\frac{T_1 + T_2}{2} - T_0\right)$ .
Case 1: $\frac{20}{7} = k(50 - 10) = 40k \Rightarrow k = \frac{1}{14}$
Case 2: $\frac{12}{t} = \frac{1}{14}(34 - 10) = \frac{24}{14}$
$t = 7$ min
So the answer is (d) $7$ .

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