Final answer:
The wooden cylinder floats with half of its length immersed in water, indicating that its density is equal to the weight of the water it displaces. Therefore, the density of wood is less than the density of water.
Step-by-step explanation:
When an object floats in water, the density of the object must be taken into account to determine its buoyancy. According to Archimedes' Principle, the buoyant force on a submerged object is equal to the weight of the fluid that the object displaces. In the case of a wooden cylinder floating vertically with half of its length immersed in water, this implies that the weight of the displaced water is equal to the weight of the cylinder. Since the cylinder floats with half of its volume submerged, it displaces an amount of water equal to half its volume, and therefore, half its weight is supported by buoyant force.
According to the principle of buoyancy and the information that wood floats, we can infer that wood must be less dense than water since it displaces only as much water as is necessary to support its weight. Hence, the density of wood in this case is less than the density of water.