Two balls, with masses $m$ and $2m$, are moving in a vacuum with initial velocities $2v$ and $v$ respectively, and they collide head-on, as illustrated. Following the collision, the ball of mass $m$ rebounds leftwards with 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$\frac{9}{2}mv^2$