Answer
$6561\;lb$.
Work Step by Step
The given values are
$F_s=81\;lb$
$r_l=9\;in.$
$r_s=1\;in.$
Formula
$\Rightarrow \frac{F_l}{F_s}=\frac{r^2_l}{r^2_s}$
Substitute all the values.
$\Rightarrow \frac{F_l}{81\;lb}=\frac{(9\;in.)^2}{(1\;in.)^2}$
Simplify.
$\Rightarrow F_l=(81\;lb)\frac{(9\;in.)^2}{(1\;in.)^2}$
$\Rightarrow F_l=6561\;lb$
Hence, the $F_l$ is $6561\;lb$.
