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# Astronomical question and answer 244

Frank L. Preuss

A man goes on the pavement in the direction towards the east. Next to him a truck also drives in the direction towards the east. Both have the same speed of 4 km per hour. The sun cast the shadow of the man upon the truck. How fast does the shadow on the truck move?

The shadow on the truck has the speed of 0 km/h.

The truck now stops and the man carries on walking and does not change his speed. How fast does the shadow of the man move?

The shadow of the man moves with a speed of 4 km/h on the truck in the direction towards the east.

The truck now moves again, but with a speed of only 1 km/h. The man carries on walking and also keeps his speed. How fast does his shadow move on the truck?

The speed of the shadow of the man on the truck is 4 km/h minus 1 km/h = 3 km/h, and also again in the direction towards the east.

The name of the man is Mr Newmoon and the truck has the inscription of his company: Planet Earth.

This is the end of "Astronomical question and answer 244"
To the German version of this chapter: Astronomische Frage und Antwort 244

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