The correct option is C 28∘C
Given that,
Temperature of surrounding, θo=10∘
θ1=60∘
θ2=40∘
Time taken to change from θ1 to θ2=7 min
According to Newton's law of cooling dθdt=−K(θ−θ0)
∫t0dt=1K∫θ2θ1−dθ(θ−θ0)
t=1Kloge[θ1−θ∘θ2−θ∘]
When temperature changes from 60∘ to 40∘
⇒7=1Kloge[60−1040−10] ...(i)
Let the the temperature after next 7 minutes is θ
⇒7=1Kloge[40−10θ−10] ...(ii)
From equation (i) and (ii)
log5030=log30θ−10
53=30(θ−10)⇒θ=28∘C
Hence, option, (c) correct