A ball of mass $200\ \text{g}$ moves at $8\ \text{m/s}$ towards a bat. The bat pushes it back with a force that changes with time as shown in the graph: it rises steadily to $600\ \text{N}$ in $5\ \text{ms}$ and falls steadily back to zero in the next $5\ \text{ms}$. The speed of the ball as it leaves the bat is

Fig. 1: Force-time graph: the force rises in a straight line from 0 to 600 N at 5 ms, and falls in a straight line back to 0 at 10 ms.