Answer
The plot will be continued in region C.
Work Step by Step
We can use equation (9-67) to write an expression for the final velocity $v_{1f}$ of block 1 after the collision:
$v_{1f} = \frac{m_1-m_2}{m_1+m_2}~v_{1i}$
If $m_1 \lt m_2,$ then $v_{1f} \lt 0$ and block 1 will move in the -x-direction after the collision. Since $-1 \lt \frac{m_1-m_2}{m_1+m_2} \lt 0$, the speed of block 1 after the collision is less than the initial speed.
Therefore, the plot will be continued in region C.
