A square board with side length $x$ is suspended freely from a nail P, as illustrated. The board is of uniform thickness and is made from material with uniform density. Another square board, with side length $2x$, is made from the same material and has the same thickness as the first board. This second board is then suspended from a nail Q. Nails P and Q are level with each other. What is the vertical distance between the positions of the centres of gravity of the two boards?
- A$0$
- B$\frac{x}{\sqrt{2}}$
- C$x$
- D$x\sqrt{2}$