A ladder hangs over the side of a ship anchored in port. The bottom rung of the ladder touches the water. The distance between rungs is 30cm, and the length of the ladder is 270cm.
If the tide is rising at a rate of 15cm per hour, how long will it be before the water reaches the top rung?
The ship will rise with the tide, so the water will always remain level with the first rung.
Why this works
This riddle plays with the concepts of buoyancy and relative motion. Although the tide is rising at a rate of 15cm per hour, the ship itself will also rise with the tide since it is floating. Therefore, the water level will always remain at the same height relative to the bottom rung of the ladder, meaning it will never reach the top rung, no matter how high the tide rises! This clever twist illustrates how floating objects behave in water, making it a fun logical challenge.