Question

A body cools from $75^{\circ}C$ to $70^{\circ}C$ in time $t_1$, from $70^{\circ}C$ to $65^{\circ}C$ in time $t_2$ and from $65^{\circ}C$ to $60^{\circ}C$ in time $t_3$, then:

• A. $ t_{3} > t_{2} > t_{1} $
• B. $ t_{1} > t_{2} > t_{3} $
• C. $ t_{2} > t_{1}= t_{3} $
• D. $ t_{1} > t_{2} = t_{3} $

Answer 1

Answer: (A)

From Newtons law of cooling
$ \frac{dH}{dt}=K\left( \frac{\theta _{1}+\theta _{2}}{2}-\theta_{0} \right) $
where $ \theta _{0} $ is temperature of surrounding,
$ \frac{\theta_{1}+\theta_{2}}{2} $
the temperature of body.
Hence, $ t_{3} > t_{2} > t_{1}. $