Newton’s law of cooling says that the rate of cooling of a body is proportional to the temperature difference between the body and its surrounding when the difference in temperature is small.
(a) Will it be reasonable to assume that the rate of heating of a body is proportional to temperature difference between the surrounding and the body (for small difference in temperature) when the body is placed in a surrounding having higher temperature than the body?
(b) Assuming that our assumption made in (a) is correct estimate the time required for a cup of cold coffee to gain temperature from `10^(@)C` to `15^(@)C` when it is kept in a room having temperature `25^(@)C`. It was observed that the temperature of the cup increases from `5^(@)C` to `10^(@)C` in 4 min

Answer

(a) Yes (b) `5.6 min`