10. (5 points) As shown in the figure, it is known that $A B=40 \mathrm{~cm}$, the curve in the figure is formed by three semicircular arcs of different radii smoothly connected. Therefore, the area of the shaded part is $\qquad$ $\mathrm{cm}^{2}$. ( $\pi$ is taken as 3.14)
【Solution】Solution: $40 \div 2=20$ (cm)
$$
\begin{array}{l}
20 \div 2=10 \text { (cm) } \\
3.14 \times 20^{2}-3.14 \times 10^{2} \div 2 \times 4 \\
=1256-628 \\
=628 \text { (square cm) }
\end{array}
$$

Answer: The area of the shaded part is 628 square cm. Therefore, the answer is: 628.