Answer
$13.96 \text{ inches}$
Work Step by Step
Arc length $s$ can be computed using the formula $s=r\theta$ where $r$ is the radius of the circle and $\theta$ is the central angle.
Here we have:
$\theta=20^{\circ}=20\times\frac{\pi}{180}\,rad=\frac{\pi}{9}\,rad$
$r=40\,inches$
Using the formula for arclength gives:
$s=40\text{ inches}\times\frac{\pi}{9}\approx 13.96 \text{ inches}$
Thus, the tip of the pendulum moves $13.96$ inches each second.
