Thermal Properties of Matter - Result Question 46

47. 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.

[NEET Odisha 2019]

(a) $15 min$

(b) $10 min$

(c) $12 min$

(d) $20 min$

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Answer:

Correct Answer: 47. (a)

Solution:

  1. (a) According to Newton’s law of cooling

$ \frac{(T_1-T_2)}{t}=K(\frac{T_1+T_2}{2}-T_0) $

$ \begin{align*} & \frac{(80-70)}{12}=K(75-25) \tag{i}\\ & \frac{(70-60)}{t^{\prime}}=K(65-25) \tag{ii} \end{align*} $

$\Rightarrow t^{\prime}=12 \times=15 min$