A steel ax and an aluminum piston have the same apparent weight in water. When they are weighed in air:
A) they weigh the same B) the ax is heavier C) the piston is heavier D) both weigh less than they did in water E) depends on their shapes
The correct answer and explanation is:
The correct answer is B) the ax is heavier.
Explanation:
When an object is submerged in a fluid like water, it experiences an upward buoyant force equal to the weight of the water displaced by the object. This buoyant force reduces the apparent weight of the object. The more the object displaces, the greater the buoyant force and the lower the apparent weight. In the case of the steel ax and aluminum piston, both have the same apparent weight in water, meaning they displace the same amount of water.
However, the density of steel is much higher than that of aluminum. This means that for the same volume, the steel ax is much heavier in air compared to the aluminum piston. In air, the buoyant force is much smaller (because the density of air is much less than water), so the full weight of the objects is felt. The ax, being made of steel, has a greater mass and therefore weighs more in air than the aluminum piston.
So, while both objects appear to have the same weight in water due to the buoyant force, when measured in air, the ax will be heavier because steel is denser than aluminum. The piston, being made of aluminum, will weigh less in air because of its lower density. Therefore, the ax is heavier in air.