A thin rectangular piece of wood floats in water. You slowly pour oil with a density equal to that of the wood on the surface of the water until the height of the oil above the water is twice the height of the piece of wood. Which statement is correct?
A) The wood floats on top of the oil, so it sticks up in the air.
B) The wood does not change its position
C) The wood sinks below the surface of the water.
D) The wood is half in the water and half in the oil.
E) The wood floats in the oil just above the water.

Question

Quizplus · Accepted Answer

Since the density of the oil is equal to that of the wood, the wood will float at the interface between the oil and water, not changing its buoyancy significantly but adjusting its position so that it floats in the oil just above the water. This is because objects float at a level where the fluid (or fluids, in this case) can provide enough buoyant force to counteract the object's weight, and since the oil and wood have the same density, the wood will float in the oil layer.

A Thin Rectangular Piece of Wood Floats in Water