Moscow Anthology/Amusing Problems/1
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- Two school students are observing a steam locomotive, the smoke from whose smokestack appears to be rising in a vertical plume.
- As they have been taking meteorological measurements, they know that the wind is steady and gust-free, and its speed is $20$ miles per hour.
- How do they know the train's speed?
Hence the smoke was travelling at the same speed as the wind.
Thus it must have been rising from a smokestack that is travelling at that same speed.