A body cools in 7 min from 60oC to 40oC. What will be its temperature after the next 7 min? The temperature of surroundings is 10oC.

According to Newton's law of cooling,θ1−θ2t=Kθ1+θ22−θ0So that 60−407=K60+402−10⇒ K=114  ………..(i)Now if after cooling from 40oC to 7 min the temperature of the body becomes θ, according to Newton's law of cooling,40−θ7=K40+θ2−10which in the light of Eq. (i), i.e., K = (1/l4), gives40−θ7=11420+θ2160−4θ=20+θ;θ=28∘C