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Suresh Kumar was rowing upstream on the Brahmaputra River. When he had covered one kilometer from his starting point, his hat fell into the river and started floating downstream. Suresh continued to row upstream for five more minutes before he realized that his hat had fallen off. He then, turned back and caught up with the hat just as it reached the starting point. Then, what is the speed of the flow of the river?

Suresh Kumar was rowing upstream on the Brahmaputra River. When he had covered one kilometer from his starting point, his hat fell into the river and started floating downstream. Suresh continued to row upstream for five more minutes before he realized that his hat had fallen off. He then, turned back and caught up with the hat just as it reached the starting point. Then, what is the speed of the flow of the river? Correct Answer 6 km/hr

Calculation:

Here, with respect to the hat, Suresh travels upstream for 5 minutes.

Therefore, he has to travel downstream for 5 minutes to reach the hat again.

It may be noted that after the hat has fallen off, the two bodies are moving in the same river with the speed of the water applicable to both, irrespective of the direction of their movement.

∴ As far as their relative motion is concerned, the speed of the water can be ignored.

In these 10 minutes, the hat has drifted with the river for 1 km.

∴ The speed of the current is 1km/10 min = 1km/(10/60)hr = 6 km/hr.

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