# A boat, which has a speed of 5km/h in still water, crosses a river of width 1km along the shortest path possible in 15 minutes. Find the velocity of the river?

##### 1 Answer

Jun 7, 2018

The river is moving at a speed of 3 km/h.

#### Explanation:

If the speed of the river is constant over the stretch that the boat is sailing, we can use Pythagoras:

If the river had been still, the boat would have moved from A to B, 1 km.

Instead, because the water is moving, the boat moves from A to C,

This stretch must be

According to Pythagoras,

Therefore

As the river, therefore, moves