A rock that weghts 10N displaces 12N of water?

Not unless somebody is holding it down.

If the rock weighs 10N and you just set it in the water, it'll sink until it displaces
10N of water, and at that point, it has no desire to sink any further.
Not unless somebody is holding it down.

If the rock weighs 10N and you just set it in the water, it'll sink until it displaces
10N of water, and at that point, it has no desire to sink any further.