Transmission Of Heat Question 175
Question: A body takes 4 minutes to cool from $ 100^{o}C $ to $ 70^{o}C $ . To cool from $ 70^{o}C $ to $ 40^{o}C $ it will take (room temperature is $ 15^{o}C $ )
[MP PET 1995]
Options:
A) 7 minutes
B) 6 minutes
C) 5 minutes
D) 4 minutes
Show Answer
Answer:
Correct Answer: B
Solution:
$ \frac{{\theta _{1}}-{\theta _{2}}}{t}=K,( \frac{{\theta _{1}}+{\theta _{2}}}{2}-{\theta _{0}} ) $
$ \
Therefore $ $ \frac{100-70}{4}=K,( \frac{100+70}{2}-15 ) $ = 60K
Therefore K = $ \frac{1}{8} $ Again $ \frac{70-40}{t}=\frac{1}{8}( \frac{70+40}{2}-15 ) $ = 5
Therefore t = 6 min.
BETA
