Answer
$11.5 \pi \ m$
Work Step by Step
Let $l$ be the length of an arc:
$l=\dfrac{\text{Measure of the arc}}{360^{\circ}} \times 2 \pi r ~~~(a)$
or, $l=\dfrac{\text{Measure of the arc}}{360^{\circ}} \times \pi d~~(b)$
Here, $r$ represents radius and $d$ is diameter.
For this arc: Angle=$180^{\circ}$ and $d=23 \ m$
Thus, equation (b) becomes:
$l=\dfrac{180^{\circ}}{360^{\circ}} \times \pi (23)=11.5 \pi \ m$
