Q.

A metallic sphere cools from 500C to 400C in 300s. If atmospheric temperature around is 200C, then the sphere’s temperature after the next 5 minutes will be close to :

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350C

330C

280C

310C

answer is 2.

(Detailed Solution Below)

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Detailed Solution

Newton's Law of Cooling, θ1−θ2t1−t2=kθ1+θ22−θsur⇒50−40300=k50+402−20⇒10300=k45−20−−−1Now, 40−θf300=k40+θf2−20−−−−−2Dividing1 by 2, 1040−θf=2540+θf2−20⇒1040−θf=25θf×2⇒θf=1003=330C

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