No to be equivalent, they must be of equal size. i.e cardinality of $O(n)$ and $O(n^2)$ must be equal i.e contain the same elements(here the elements are the functions), that means $O(n)$ must contain all the functions which are in $O(n^2)$, I showed that $5n^2$ $\in$ $O(n^2)$
but $5n^2$ $\notin$ $O(n)$. Hence $O(n)$ and $O(n^2)$ are not equivalent.