A body cools in 7 min from 60∘C to 40∘C. What will be its temperature after the next 7 min ?
The temperature of surroundings is 10∘C. [Assume Newton's Law of cooling is applicable]
A
T=32∘C
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B
T=28∘C
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C
T=24∘C
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D
T=36∘C
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Solution
The correct option is BT=28∘C Using Newton's Law of cooling. (T1−T2t)=K[(T1+T22)−T0]
⇒(60−407×60)=K[(60+402)−10]
⇒(207×60)=K×40................(I)
Let the final temperature by T∘C
(40−T7×60)=K[(40+T2)−10]
(40−T7×60)=K[20+T2].....(II)
dividing Eq.(I) to Eq.(II)
⇒160−4T=20+T ⇒T=28∘C
Hence, option (b) is the correct answer.