A hot body, obeying Newtons law of cooling is cooling down from its peak value 80°C to an ambient temperature of 30°C. It takes 5 minutes in cooling down from 80°C to 40°C. [JEE ONLINE 11-04-2014] |
How much time will it take to cool down from 62°C to 32°C? |
(Given In 2 = 0.693, In 5 = 1.609) |
A) 3.75 minutes
B) 8.6 minutes
C) 9.6 minutes
D) 6.5 minutes
Correct Answer: B
Solution :
[b] From Newtons law of cooling, |
From question and above equation, |
(1) |
and (2) |
Dividing equation (2) by (1), |
On solving we get, time taken to cool down from 62°C to 32°C, t = 8.6 minutes. |
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