Thermal Properties of Matter - Result Question 49
50. A body cools from $50.0^{\circ} C$ to $48^{\circ} C$ in $5 s$. How long will it take to cool from $40.0^{\circ} C$ to $39^{\circ} C$ ? Assume the temperature of surroundings to be $30.0^{\circ} C$ and Newton’s law of cooling to be valid.
(a) $2.5 s$
(b) $10 s$
(c) $20 s$
(d) $5 s$
[1994]
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Answer:
Correct Answer: 50. (b)
Solution:
- (b) Rate of cooling $\propto$ temperature difference between system and surrounding.
As the temperature difference is halved, so the rate of cooling will also be halved.
So time taken will be doubled
$t=2 \times 5$ sec. $=10$ sec.
