Q. A body takes $5\ minutes$ to cool from $90℃$ to $60℃$. If the temperature of the surroundings is $20℃$, the time taken by it to cool from $60℃$ to $30℃$ will be
A) $5\ min$
B) $8\ min$
C) $11\ min$
D) $12\ min$
Explanation
(c) $\frac{90 - 60}{5} = K\left( \frac{90 + 60}{2} - 20 \right) \Rightarrow 6 - K \times 55 \Rightarrow K - \frac{6}{55}$
And, $\frac{60 - 30}{t} = \frac{6}{55}\left( \frac{60 + 30}{2} - 20 \right) \Rightarrow t = 11$ minute
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.