Two spheres of the same metal have radii $r$ and $2r$. They are heated to the same temperature and placed in the same environment. The ratio of their rates of cooling will be:

Hot water cools from $60\,^oC$ to $50\,^oC$ in the first $10\,minutes$ and to $42\,^oC$ in the next $10\,minutes.$ The temperature of the surroundings is ...... $^oC$

$A$ sphere,a cube,and a disc,all of the same material,quality,and volume,are heated to $600\,^{\circ}C$ and left in air. Which of these will have the lowest rate of cooling?

The instantaneous temperature difference between a cooling body and its surroundings,which obeys Newton's law of cooling,is $\theta$. Which of the following graphs represents the variation of $\ln \theta$ with time $t$?

$A$ liquid cools down from $70^{\circ}C$ to $60^{\circ}C$ in $5$ minutes. The time taken to cool it from $60^{\circ}C$ to $50^{\circ}C$ will be

Four spheres $A, B, C$ and $D$ are of the same radius but made of different metals. Their densities are in the ratio $6 : 3 : 4 : 5$ and specific heats are in the ratio $2 : 5 : 4 : 6$. These are initially kept at the same temperature and placed in the same surroundings. The sphere which has the slowest rate of cooling is