\[R = 24\ см;\ \ \ a = 40\ мин:\]
\[1)\ a = 360{^\circ} \bullet \frac{40}{60} = 240{^\circ}.\]
\[2)\ L = \frac{\pi\text{Ra}}{180{^\circ}} = \frac{24\pi \bullet 240{^\circ}}{180{^\circ}} = 32\pi.\]
\[Ответ:\ \ 32\text{π\ }см.\]