A ferry boat loaded with rocks has to pass under a bridge. The maximum height of the rocks is slightly more than the height of the bridge so that the boat just fails to pass under the bridge. Should some of the rocks be removed or some more rocks be added?

Question

A ferry boat loaded with rocks has to pass under a bridge. The maximum height of the rocks is slightly more than the height of the bridge so that the boat just fails to pass under the bridge. Should some of the rocks be removed or some more rocks be added?

Philoid · Accepted Answer

Here, we need the boat to immerse a bit more in the water so that it passes easily. To do this, we need to displace more water from beneath it. This can be done by adding more rocks to it, which will increase its mass and thus will displace more water.