MHTCET 18 Apr 2026 Shift 1 Paper

Concept:Newton's law of cooling states that the rate of cooling is proportional to the excess temperature of the body above its surroundings.So excess temperature follows exponential decay, and the time to halve the excess temperature remains constant.Explanation:Surrounding temperature is $T_s = 20^{\circ}C$.Initial body temperature is $100^{\circ}C$.Initial excess temperature is $100 - 20 = 80^{\circ}C$.After $20$ minutes, the body cools to $60^{\circ}C$.Excess temperature then is $60 - 20 = 40^{\circ}C$.Thus, in $20$ minutes, the excess temperature halves from $80^{\circ}C$ to $40^{\circ}C$.Now, when the body cools to $40^{\circ}C$, excess temperature becomes $40 - 20 = 20^{\circ}C$.This is again half of $40^{\circ}C$.Therefore, the second halving will also take $20$ minutes.Total time taken is $20 + 20 = 40$ minutes.Answer:The total time taken is $40$ minutes.Correct option: B.