Let $PQRS$ be a rhombus with $\angle QPS=100^{\circ }$. Let $M$ be the midpoint of $\overline{RS}$, and let $N$ be the point on $\overline{QM}$ such that $\overline{PN}$ is perpendicular to $\overline{QM}$. What is the degree measure of $\angle QNR$?