A cup of tea cools from 65.5^o C to 62.5 ^o C in one minute in a room of 22.5 ^o C . How long will s

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10-2.Transmission of Heat

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A cup of tea cools from $65.5^o C to 62.5 ^o C$ in one minute in a room of $22.5 ^o C$. How long will the same cup of tea take, in.............. minutes, to cool from $46.50^o C to 40.5 ^o C$ in the same room ? (choose nearest value)

A

$1$

B

$2$

C

$3$

D

$4$

Solution

(d) $\frac{{65.5 – 62.5}}{1} = K\left( {\frac{{65.5 + 62.5}}{2} – 22.5} \right)$ ==> $K = \frac{3}{{41.5}}$

And again $\frac{{46.5 – 40.5}}{t} = \frac{3}{{41.5}}\left( {\frac{{46.5 + 40.5}}{2} – 22.5} \right)$

==> $\frac{6}{t} = \frac{3}{{41.5}} \times 21$ ==> $t = \frac{{82}}{{21}}\tilde – 4$ $minute.$

Standard 11

Physics

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