Question

You have a small piece of iron at 25 °C and place it into a large container of water at 75 °C. Which of these could be the temperature of the water after 10 minutes?
Responses
A 25 °C25 °C
B 30 °C30 °C
C 75 °C75 °C
D 80 °C80 °C

Answer 1

C — 75 °C.

Reason: heat flows from the hot water to the colder iron, so the water cannot end up hotter than 75 °C. Because the water is a large thermal reservoir, the small iron will warm up while the water's temperature will barely change, so it can stay essentially 75 °C. The much lower values (25 or 30 °C) would require the water to lose a lot of heat to the iron, and 80 °C would require heat flow from colder to hotter, both impossible in this situation.