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The man is walking down the sidewalk in the evening, at a constant speed. As he walks away from the streetlight, he casts a shadow in front of him.
If a second man were to try and keep up with the very front tip of his shadow, would he be walking at a constant speed, accelerating or decelerating, or what?
How do you know your answer is correct?
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Slow train: a puzzle by @peterrowlett.
Can you solve it?