A cup of coffee cools from 9 0 ∘ C to 8 0 ∘ C in t minutes when the room temperature is 2 0 ∘ C . The time taken by the similar cup of coffee to cool from 8 0 ∘ C to 6 0 ∘ C at the same room temperatu

Question

A cup of coffee cools from 9 0 ∘ C to 8 0 ∘ C in t minutes when the room temperature is 2 0 ∘ C . The time taken by the similar cup of coffee to cool from 8 0 ∘ C to 6 0 ∘ C at the same room temperature is :

TestHub · Accepted Answer

By using average form of Newton's law of cooling ​ t 90 − 80 ​ = k ( 2 90 + 80 ​ − 20 ) t ′ 80 − 60 ​ = k ( 2 80 + 60 ​ − 20 ) ​ ​ (i)/(ii) t × 20 10 × t ′ ​ = 50 65 ​ t ′ = 50 65 ​ × 2 t = 25 65 ​ t = 5 13 ​ t ​

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