Question

A beaker full of hot water is kept in a room and it cools from
I) 90${}^o$C to 80${}^o$C in $t_1$ sec.
II) 80${}^o$C to 70${}^o$C in $t_2$ sec.
III) 70${}^o$C to 60${}^o$C in $t_3$ sec.
IV) 60${}^o$C to 50${}^o$C in $t_4$ sec.
If the room temperature is 10${}^0$C. Identify the order in which the time of cooling increases

• A. IV,III,II & 1
• B. I,III,IV & II
• C. I, II,III & IV
• D. III, I, II & IV

Answer 1

Answer: (C)

I, II,III & IV

According to Newton's cooling law rate of cooling increases as temperature difference between body and surrounding increases. Here each body is cooling by same temperature gap[${10}^{0}C$], but absolute temperature difference of body [($90-10$) ${}^{0}C$ etc] goes on decreasing from option 1 to option 4 hence time of cooling goes on increasing.

Hence answer is $t_1<t_2<t_3<t_4$