A 6-cm cube of plastic floats in water with 1 cm of the cube above the water.What is the density of the cube? A)1.0 g/cm³ B)0.8 g/cm³ C)1.2 g/cm³ D)0.5 g/cm³ E)0.6 g/cm³

Question

Quizplus · Accepted Answer

The volume of the cube is 6 cm x 6 cm x 6 cm = 216 cm^3. 
Since 1 cm of the cube is above the water, the volume of the cube submerged in water is 5 cm x 5 cm x 5 cm = 125 cm^3. 
The buoyant force on the cube is equal to the weight of the water displaced by the cube. 
Since the cube floats, the buoyant force is equal to the weight of the cube, which is equal to its density times its volume. 
Therefore, density = weight/volume = buoyant force/volume = weight of water displaced/volume of displaced water = 1 g/cm^3 (density of water). 
The density of the cube is therefore the same as the density of water, which is 0.8 g/cm^3.

A 6-Cm Cube of Plastic Floats in Water with 1