A calorimeter of mass 0.2 kg and specific heat 900 J/kg-K . Containing 0.5 kg of a liquid of specifi

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10-2.Transmission of Heat

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A calorimeter of mass $0.2$ kg and specific heat $900 J/kg-K$ . Containing $0.5$ kg of a liquid of specific heat $2400J /kg-K$ . Its temperature falls from ${60^o}C\,{\rm{to}}\,\,{\rm{5}}{{\rm{5}}^{\rm{o}}}C$ in one minute. The rate of cooling is ....... $J/s$

A

$5$

B

$15$

C

$100$

D

$115$

Solution

(d) Rate of cooling (here it is rate of loss of heat)

$\frac{{dQ}}{{dt}} = (mc + W)\frac{{d\theta }}{{dt}} = ({m_l}{c_l} + {m_c}{c_c})\frac{{d\theta }}{{dt}}$

==> $\frac{{dQ}}{{dt}} = (0.5 \times 2400 + 0.2 \times 900)\left( {\frac{{60 – 55}}{{60}}} \right)$$ = 115\;\frac{J}{{\sec }}$.

Standard 11

Physics

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(IIT-1991)