Simply \newpage
or \pagebreak
will work, e.g.
hello world
\newpage
```{r, echo=FALSE}
1+1
```
\pagebreak
```{r, echo=FALSE}
plot(1:10)
```
This solution assumes you are knitting PDF. For HTML, you can achieve a similar effect by adding a tag <P style="page-break-before: always">
. Note that you likely won't see a page break in your browser (HTMLs don't have pages per se), but the printing layout will have it.