Old time mills

Old time mills for grinding wheat or corn into flour were often powered by a water wheel. Some water wheels had water falling over paddles, other water wheels dipped their paddles in a moving river, which as it flowed past turned the wheel. One particular mill has a water wheel with radius $$3~\mbox{m}$$ suspended above a river such that the bottom edge of the paddles are just in contact with and move with the river water. If the river flows at $$0.5~\mbox{m/s}$$ then what is the period of the spinning water wheel?

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