Transmission Of Heat Question 303
Question: A body takes 5 minute to cool from $ 80{}^\circ C $ to $ 50{}^\circ C $ . How much time it will take to cool from $ 60{}^\circ C $ to $ 30{}^\circ C $ , if room temperature is $ 20{}^\circ C $ .
Options:
A) 40 minute
B) 9 minute
C) 30 minute
D) 20 minute
Show Answer
Answer:
Correct Answer: B
Solution:
According to Newtons law of cooling in first case,$ \frac{80-50}{5}=K[ \frac{80+50}{2}-20 ] $ ..(i) in second case,$ \frac{60-30}{t}=k[ \frac{60+30}{2}-20 ] $ (ii) Dividing equation (i) by (ii) we get, $ \frac{t}{2}=\frac{45}{25} $
$ \Rightarrow $ $ t=9 $ min.
BETA
