A body cools in 7 minutes from {60^o}C to {40^o}C What time (in minutes) does it take to cool from {

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10-2.Transmission of Heat

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A body cools in $7$ minutes from ${60^o}C$ to ${40^o}C$ What time (in minutes) does it take to cool from ${40^o}C$ to ${28^o}C$ if the surrounding temperature is ${10^o}C$? Assume Newton’s Law of cooling holds

A

$3.5$

B

$11$

C

$7$

D

$10$

Solution

(c) In first case $\frac{{60 – 40}}{7} = K\left[ {\frac{{60 + 40}}{2} – 10} \right]$….$(i)$

In second case $\frac{{40 – 28}}{t} = K\left[ {\frac{{40 + 28}}{2} – 10} \right]$….$(ii)$

By solving $t = 7$ $minutes$

Standard 11

Physics

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