A block of mass $5\ \text{kg}$ is at rest at $x = 0$ on a smooth horizontal floor. A horizontal force F acts on it along the x-axis, and F changes with the position of the block as shown in the graph. What is the speed of the block when it reaches $x = 8\ \text{m}$?

Fig. 1: Force against position: rising from 0 to 20 N between 0 and 2 m, steady at 20 N from 2 to 5 m, falling to 0 at 7 m, then -10 N from 7 to 8 m.