Question

The temperature of a liquid drops from 365K to 361K in 2 minute. The time during which temperature of the liquid drops from 344K to 342 K is (temperature of room is 293K) –

• A. 84 sec
• B. 72 sec
• C. 66 sec
• D. 60 sec

Answer 1

Answer: (A)

84 sec

Answer 2

From newton's law of cooling

$\frac{365 - 361}{2}$ = K $\left( \frac{365 + 361}{2} - 293 \right)$ …..(1)

$\frac{344 - 342}{t}$ = K $\left( \frac{344 + 342}{2} - 293 \right)$ …...(2)

(1) / (2)

t = $\frac{365 + 361 - 586}{344 + 342 - 586}$ = $\frac{140}{100}$ min.

= $\frac{140 \times 60}{100}$ sec = 84 sec