Q. Certain quantity of water cools from 70°C to 60°C in the first 5 minutes and to 54°C in the next 5 minutes. The temperature of the surroundings is :
A) 45°C
B) 20°C
C) 42°C
D) 10°C
Explanation
[Solution] Newton's law with average temperatures: $\frac{10}{5} = k(65 - T_0)$ and $\frac{6}{5} = k(57 - T_0)$. Dividing, $\frac{5}{3} = \frac{65 - T_0}{57 - T_0} \Rightarrow T_0 = 45$°C. Answer (1).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.