Multiple choice

Sally wants to cross the river. She heads directly across the river at the speed of 10 km/hr. The river is flowing at the speed of 6 km/hr. What is the resultant speed of her boat?

  1. 30 km/hr

  2. 11.7 km/hr

  3. 20 km/hr

  4. 10 km/hr
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The resultant speed is the vector sum of the two perpendicular velocities. Resultant = sqrt(10^2 + 6^2) = sqrt(100 + 36) = sqrt(136). sqrt(136) is approximately 11.66, which rounds to 11.7.

AI explanation

To find the resultant speed of the boat moving perpendicularly across a flowing river, apply the Pythagorean theorem to the boat's heading speed and the river current speed. The calculation is the square root of (10 squared plus 6 squared). This results in the square root of 136, which is approximately 11.7 km/hr.

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