Q. The temperature of a body in air falls from $40^\circ$C to $24^\circ$C in 4 minutes. The temperature of the air is $16^\circ$C. The temperature of the body in the next 4 minutes will be:
A) $\frac{14}3\,^\circ$C
B) $\frac{42}3\,^\circ$C
C) $\frac{28}3\,^\circ$C
D) $\frac{56}3\,^\circ$C
Explanation
[Solution by Dr. Abubacker] Newton's law (average-temperature form): $\frac{40-24}4=k\left(\frac{40+24}2-16\right)\Rightarrow k=\frac14$ per minute. Next 4 min: $\frac{24-T}4=\frac14\left(\frac{24+T}2-16\right)\Rightarrow48-2T=T-8\Rightarrow T=\frac{56}3\,^\circ$C. Answer (4).
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.