Question

When placed in air at ${30}^{\circ }C,$ the temperature of a body decreases from ${60}^{\circ }C\text{to}{50}^{\circ }C$ in ten minutes. After next ten minutes, its temperature will be-

• A. Less than ${40}^{\circ }C$
• B. ${40}^{\circ }C$
• C. More than ${40}^{\circ }C$
• D. Not definite

Answer 1

The correct option is C More than ${40}^{\circ }C$

From Newton's law of cooling.
$\frac{dT}{dt}=-k[T_{avg.}-T_s]$
rate of cooling $\propto$ rate of temperature difference
As $T_{avg}.$ in Case- I > $T_{avg}.$ in Case - II
Hence, temperature will become more than ${40}^{\circ }$ in next 10 minutes.