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An object kept in a large room having air temperature of $25^\circ C$ takes 12 minutes to cool from $80^\circ C$ to $70^\circ C$. The time taken to cool for the same object from $70^\circ C$ to $60^\circ C$ would be nearly:
Detailed Solution
$\frac{T_1-T_2}{t}=K\left(\frac{T_1+T_2}{2}-T_s\right)$. First: $\frac{10}{12}=K(75-25) \Rightarrow K=\frac{1}{60}$. Second: $\frac{10}{t}=\frac{1}{60}(65-25) \Rightarrow t=15$ min.