A body is 20 K warmer than the room. It cools by Newton's law, and its excess falls to 10 K in 6.0…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A body is warmer than the room. It cools by Newton's law, and its excess falls to in minutes. How long until the excess is ? What is the excess after minutes?
Need a reminder? The key ideaShow
Newton's law of cooling: , so . Over a short interval, the rate is in proportion to the average excess over the surroundings.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. From to takes minutes; from to takes another : minutes in all.
Step 2. After minutes, one and a half halvings: .
Answer: minutes; .
Watch out. Exponential decay does not fall by the same number of kelvin each minute; it falls by the same fraction.
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