A board has a mass of 750 g. If you ground the whole board down to sawdust, what would be the mass of the pile of sawdust?

The answer is 750 grams

The correct answer is exactly 750 g.

Since the mass of board is 750 g, the mass of the pile of sawdust after the whole board is ground down is 750 g.

This is according to the Law of conservation of mass. According to this law, matter can neither be created nor destroyed by any physical transformations or chemical reactions. In any chemical reaction the mass of the products is equal to the mass of the reactants.

Here the board undergoes a physical transformations from being a whole board to a pile of sawdust. Thus according to the Law of conservation of mass, the mass of the whole board will be equal to the mass of a pile of sawdust.