Suppose you bought a cup of coffee each morning on your way to school. You wish to drink the coffee when you reach your class and have time to settle down which is about 30 minutes from the time of purchase. You like to add cream to your coffee, but you still want the coffee to be as hot as possible after those thirty minutes. Therefore, should you add the cream at the time of purchase or after about 15 minutes? What do you predict? Will the coffee be hotter if you add the cream earlier or if you add it later? What is the reason for your prediction?

Question

Physics

Guest

6 July, 06:00

Suppose you bought a cup of coffee each morning on your way to school. You wish to drink the coffee when you reach your class and have time to settle down which is about 30 minutes from the time of purchase. You like to add cream to your coffee, but you still want the coffee to be as hot as possible after those thirty minutes. Therefore, should you add the cream at the time of purchase or after about 15 minutes? What do you predict? Will the coffee be hotter if you add the cream earlier or if you add it later? What is the reason for your prediction?

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Answers (2)

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Lena · Answer 1

Cream should be added at the time of purchase of coffee. It will lower the temperature of the content. So rate of cooling gets reduced. Hence lesser heat will come out during 15 minutes of cooling. We all know, rate of cooling is at higher speed if temperature difference of hot body and surrounding is greater.

Leticia Michael · Answer 2

As we add the cream to the coffee, the rate of cooling is decreased as the cream contains lots of air pockets trapped in it. Air is the bad conductor of heat, so the layer of cream acts as an insulator and the rate of cooling of cream is lowered.

Now according to the Newton's law of cooling, as the temperature difference is more between the surrounding and the coffee, rat of cooling is more so add the cream initially to the coffee, so that the rate of cooling decreases.