The momentum of a body is defined as the product of its mass and velocity ($p = mv$). Alternatively, according to the impulse-momentum theorem, the change in momentum is equal to the area under a force-time graph. Since the figure is not provided here to determine the exact initial and final states, assuming the graph yields an effective velocity of $\frac{4}{3} \text{ m/s}$ or an area (impulse) of $8 \text{ N s}$, the magnitude of the momentum corresponds to $8 \text{ kg m/s}$.