Question

A piece of wood is floating in a tub of water. A second piece of wood rest on top of the first piece; it does NOT touch the water. If the second piece is removed from the first and placed in the water, what happens to the water level in the tub?

•	The water level cannot be determined without additional information.
•	The water level remains unchanged.
•	The water level rises.
•	The water level drops.

Answer 1

Initially the weight of the wood pieces were was counter-balanced by the upthrust provided by water which depended upon the volume of first piece of wood that was inside the water (which was equal to the volume of water displaced).

Now when the second piece was placed in the water then again the the weight of both the blocks individualy (which doesn't change) would be counter-balanced by the upthrust of total volume (coming from contribution from both the blocks) which would be same as earlier.

Hence the level of water would remain unchanged.