Q.
Certain quantity of water cools from 70°C to 60°C in the first 5 minutes and to 54 °C in the next 5 minutes. The temperature of the surroundings is:
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a
45°C
b
20°C
c
42°C
d
10°C
answer is A.
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Detailed Solution
By newton's law of coolingθ1-θ2t=kθ1+θ22-θ0 ⇒ 70-605=k70+602-θ0 ⇒ 2=k65-θ0 ..(i) and 60-545=k 60+542-θ0 ⇒ 65=k57-θ0 ..(ii)By dividing eqn.(i) by eqn.(ii) we have 106=65-θ057-θ0⇒θ0=45o
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