Question

A swimmer jumps from a bridge over a canal and swims 1 km upstream. After that first kilometer, he passes a floating cork. He continues swimming for another half an hour and then turns around and swims back to the bridge in 30 minutes. The swimmer and the cork arrive at the bridge at the same time. The swimmer has been swimming with constant speed. How fast does the water in the canal flow?
1. 1 km/hr
2. 2 km/hr
3. 0.5 km/hr
4. 1.5 km/hr
5. 3 km/hr

Answer 1

Correct Answer - Option 1 : 1 km/hr

Given: The swimmer and the cork reached the bridge at the same time and initial distance of the cork from the bridge = 1 km.

Concept:

Going along the stream, resultant speed = speed of the boat in still water + speed of the stream.

Going against the stream, resultant speed = speed of the boat in still water - speed of the stream.

Calculations:

Here, we don’t need to calculate the speed of the swimmer.

From the given information, it is obvious that the cork took (30 + 30) = 60 minutes to reach the bridge.

Also, it is very obvious that cork will flow only with the flow of the river.

So, speed of the cork = speed of the river flow

Initial distance of the cork from the bridge = 1 km.

Speed of the cork = 1 km/1 hr = 1 km/hr