Question

A body cools from $70$${}^o$C to $60$${}^o$C in $8$ minute. The same body cools from $60$${}^o$C to $50$${}^o$C in

• A. $8$ minute
• B. less than $8$ minute
• C. More than $8$ minute
• D. $1$ or $2$ or $3$, depending on the specific heat of the body

Answer 1

Answer: (C)

More than $8$ minute

Newton's law of cooling is $\frac{d\theta }{dt}=-k(\theta -{\theta }_0)$ .In the given question we have assumed that surrounding temperature is less than $50$${}^{0}C$. As the temperature difference between body and surrounding decreases, rate of cooling decreases and time of cooling increases. Thus time will be more than 8 minutes.