# The temperature of a solid falls from $\;72^{0}C\;$ to $\;60^{0}C\;$ in 10 minutes . How much time will it take to cool from $\;60^{0}C\;$ to $\;52^{0}C\;$ if the temperature of surroundings is $\;36^{0}C\;$ c ?

$(a)\;5\;min\qquad(b)\;10\;min\qquad(c)\;15\;min\qquad(d)\;20\;min$

## 1 Answer

Answer : $\;15 \;min$
Explanation :
$\large\frac{dT}{dt} = K (\large\frac{\theta_{1}+\theta_{2}}{2} - \theta_{s})$
$\large\frac{12}{10} = K (66-36)$----(1)
$\large\frac{12}{t} = K (56 -36)$----(2)
$\large\frac{t}{10} = \large\frac{30}{20}$
$t = 15\;mins.$
answered Apr 8, 2014 by

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