Explanation:
All matter has mass and occupies space. Volume is a measure of how much space an object occupies. ... "Mass" only depends on how much matter is in an object. "Weight", on the other hand, depends on how strongly gravity pulls on an object.
They have the same density because a material, no matter how much of it there is, will always be a certain density. A 40g ball of iron has the same density as a 1g ball of iron.
The first is Design Process, the second is To see if the design solves the problem