Answer to Question #2379 in Mechanics | Relativity for Angela

Question

A stream is flowing at a speed of 3.0km/h relative to the bank. A boy who can swim at 2.0km/h in still water enters the stream and proceeds to swim downstream. At a certain point he is approaching a boat going upstream. The boat has a speed of 20km/h relative to the stream. To an observer on the shore, the boat and the boy are approaching each other at a speed of?

Answer 1

The speed of& the boy relative to a stream is& 2 km/h, relative to the observer& - 2 + 3 = 5 km/h, the speed of the boat relative to the observer is 20 - 3 = 17 km/h.
Thus the boy approaches the boat at speed of 5 km/h and the boat approaches the boy at a speed of 17 km/h relarive to the observer on the shore.