Two metallic spheres ${S_1}$ and ${S_2}$are made of the same material and have identical surface finish. The mass of ${S_1}$ is three times that of ${S_2}$. Both the spheres are heated to the same high temperature and placed in the same room having lower temperature but are thermally insulated from each other. The ratio of the initial rate of cooling of ${S_1}$ to that of ${S_2}$ is

A black body calorimeter filled with hot water cools from $60^o C$ to $50^o C$ in $4 \,\,min$ and $40^o C$ to $30^o C$ in $8 \,\min$. The approximate temperature of surrounding is  …….. $^oC$

The top of a lake gets frozen at a place where the surrounding air is at a temperature of $-20\,^oC$. Then

There are two spherical balls $A$ and $B$ of the same material with same surface, but the diameter of $A$ is half that of $B$. If $A$ and $B$ are heated to the same temperature and then allowed to cool, then

The rates of cooling of two different liquids put in exactly similar calorimeters and kept in identical surroundings are the same if