Multiple choice

A girl was travelling in a boat, suddenly wind starts blowing and blows her hat and started floating back downstream. The boat continued to travel upstream for 12 more minutes before she realized that her hat had fallen off. She turned back downstream and she caught her hat as soon as she reached the starting point. If her hat flew off exactly 2 km from where she started. What is the speed of the water?

  1. 12

  2. 8

  3. 5

  4. 9

  5. 10
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This is a classic relative motion problem. The hat and boat separate when hat falls, then reunite when boat returns. The time boat spends away from hat equals 12 min upstream + 12 min downstream = 24 min = 0.4 hours. In this time, hat floats 2 km at water speed. So water speed = 2/0.4 = 5 km/h. The elegance is that boat speed cancels out - only separation time matters.

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