[ [motion problems ]

A swimmer is swimming upstream against the current of the Neva River. Near the Palace Bridge, he lost an empty flask. After swimming another 20 minutes against the current, he noticed the loss and turned back to catch up with the flask; he caught up with it near the Lieutenant Schmidt Bridge. What is the speed of the current of the Neva River, if the distance between the bridges is 2 km?

#
Relative to the flask, the swimmer moves at a constant speed in both directions, so he will catch up with the flask in 20 minutes. Therefore, the current "travels" 2 km in 40 minutes.

## Answer

3 km $/$ h.