4. The dimensions of a king-size waterbed are 2.1m, 1.8m, and 23 cm. Find the volume and mass of the water it contains when full.

Answer 1

The mattress is shaped, more or less, like a rectangular prism. Use that formula for the volume.

Multiply the three numbers together (with the thickness in meters, not cm), to get the volume in cubic meters.

Then multiply the volume by the density of water, which is 1000 kg/m^3

That will give you the mass of the water in the mattress. The water will weigh much more than the mattress cover that contains it.