An object is cooled from 75°C to 65°C in 2 minutes in a room at 30°C . time taken to coo

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10-2.Transmission of Heat

medium

An object is cooled from $75°C$ to $65°C$ in $2$ minutes in a room at $30°C$ . The time taken to cool another object from $55°C$ to $45°C$ in the same room in minutes is

$4$

$5$

$6$

$7$

Solution

(a) According to Newton’s law of cooling
in first case, $\frac{{75 – 65}}{t} = K\left[ {\frac{{75 + 65}}{2} – 30} \right]$…..$(i)$
in second case,$\frac{{55 – 45}}{t} = K\left[ {\frac{{55 + 45}}{2} – 30} \right]$…..$(ii)$
Dividing eq. $(i)$ by $(ii)$ we get $\frac{{5t}}{{10}} = \frac{{40}}{{20}}$==>$t = 4$minutes

Standard 11

Physics

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hard

An object is cooled from $75°C$ to $65°C$ in $2$ minutes in a room at $30°C$ . The time taken to cool another object from $55°C$ to $45°C$ in the same room in minutes is

Solution

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