A hot body, obeying Newton’s law of cooling is cooling down from its peak value 80∘C to an  ambient temperature of 30∘C .It takes 5 minutes in cooling down from 80∘C to  40∘C. How much time will it take to cool down from  62∘C to  32∘Cin minutes? (Given In2=0.693, In 5=1.609)

From Newton’s law of cooling,t=1kloge⁡θ2−θ0θ1−θ0 From question and above equation,5=1kloge(40−30)(80−30) And, t= 1kloge(32−30)(62−30)Dividing equation (2) by (1),t5=1kloge(32−30)(62−30)1kloge(40−30)(80−30) On solving we get, time taken to cool down from  62∘C to  32∘C, t=8.6 minutes