A boat is rowed perpendicular to river flow at 4.5 km h⁻¹ relative to water. The river flows at 6 km h⁻¹. The speed of the boat relative to ground, in m s⁻¹, is:
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Question

A boat is rowed perpendicular to river flow at 4.5 km h⁻¹ relative to water. The river flows at 6 km h⁻¹. The speed of the boat relative to ground, in m s⁻¹, is:

G1 Physics · Accepted Answer

Boat velocity relative to water is 4.5 km h⁻¹ perpendicular to the river, while current is 6 km h⁻¹. Ground speed=√(4.5²+6²)=7.5 km h⁻¹=7.5×5/18≈2.1 m s⁻¹. Hence option B.