My question is how does google ads work when you point to a product which consists of serveral sub pages within a site. for example doing an adword for dust control and extraction, but there is a seperate page for each. but they are joined within a sub menu i.e. dust products - dust control - dust extraction would you need a seperate ad for each landing page, or os google clever enough to dig through the sub menu pages?
no, google won't dig through your sub menu pages. You'll have to create a separate ad (using same ad text if you want) for each destination URL