Question

Two identical cups of cocoa are sitting on a table. One has a metal spoon in it and one doe snot. After five minutes, which is cooler, and why?

Answer 1

The cup with the spoon in it will cool faster.

Explanation:

Let us assume the initial temperatures of both the cups to be the same.this type of a system is known as an open system where both energy and matter can flow out.Since the temperature of the air above the liquid surface is less than the liquid heat will flow from the
liquid to the air above.Now if one adds a metal spoon to a cup there will be a temperature gradient along the length of the spoon

From the figure we can say that the temperature at point 1 on the spoon is greater than that at point 2.So heat flows from point one to the other end of the spoon further reducing the temperature when compared to the other cup