As illustrated, two balls of masses $m$ and $2m$ move through a vacuum with initial velocities $2v$ and $v$ respectively and collide head-on. After the impact, the ball with mass $m$ rebounds to the left at velocity $v$. What is the loss of kinetic energy in the collision?
- A$\frac{3}{4}mv^2$
- B$\frac{3}{2}mv^2$
- C$\frac{9}{4}mv^2$
- D$\frac{9}{2}mv^2$