FILE No.192Unsolved
A boat loaded with stones floats on a pond. All the stones on the boat were thrown into the pond. The boat stays afloat, and the stones sink to the bottom of the pond.
What happens to the water level of the pond?
If you get stuck, open the hints one at a time, in order.
How much water do the stones on the boat displace?
How much water do the stones at the bottom of the pond displace?
Are stones heavier or lighter than water?
What happens to the water level of the pond?
Choose the answer closest to the truth.
It falls
The answer is "It falls."
While the stones are on the boat, they displace a weight of water equal to their weight. Once sunk in the pond, they displace only a volume of water equal to their own volume. Stones are denser than water, so that volume of water is less, and the level falls.
If the stones floated, there would be no change, but these sink.
Because you assume that putting stones in makes the water increase.
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