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

Ice is used in a cooler in order to cool its contents. Which of the following will speed up the cooling process?

A hot body, obeying Newton's law of cooling is cooling down from its peak value $80\,^oC$ to an ambient temperature of $30\,^oC$ . It takes $5\, minutes$ in cooling down from $80\,^oC$ to $40\,^oC$.  ……..  $\min.$ will it take to cool down from $62\,^oC$ to $32\,^oC$ ? (Given $ln\, 2\, = 0.693, ln\, 5\, = 1.609$)

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  …….. $^oC$

A container with $1 kg$ of water in it is kept in sunlight, which causes the water to get warmer than the surroundings. The average energy per unit time per unit area received due to the sunlight is $700 Wm ^{-2}$ and it is absorbed by the water over an effective area of $0.05 m ^2$. Assuming that the heat loss from the water to the surroundings is governed by Newton's law of cooling, the difference (in ${ }^{\circ} C$ ) in the temperature of water and the surroundings after a long time will be. . . . . . . . (Ignore effect of the container, and take constant for Newton's law of cooling $=0.001 s ^{-1}$, Heat capacity of water $\left.=4200 J kg ^{-1} K ^{-1}\right)$