The gravitational attraction $F$ on a body a distance $r$ from the center of Earth, where $r$ is greater
than the radius of Earth, is a function of its mass $m$ and the distance $r$ as follows:
$$F=\frac{m g R^{2}}{r^{2}}$$
where $R$ is the radius of Earth and $g$ is the force of gravity $-$ about 32 feet per second per second (ft per $\sec ^{2} ) .$
a. Find and interpret $F_{m}$ and $F_{r}$ .
b. Show that $F_{m}>0$ and $F_{r}<0 .$ Why is this reasonable?