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The rope ladder and the rising tide

riddlephysicsassumptionsclassic

A rope ladder hangs over the side of a boat moored in a harbour. The rungs are 20 cm apart and the bottom rung just touches the water. The tide is coming in and the water rises 60 cm every hour.

After three hours, how many rungs are under water?

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What does a boat do when the water rises?

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