The diagram represents a particle X, with kinetic energy $E_k$, moving towards a collision with a stationary particle Y. The two particles are of equal mass. Following the collision, X and Y continue together as one larger particle. How much kinetic energy is lost in the collision?
- A$0$
- B$\frac{E_k}{4}$
- C$\frac{E_k}{2}$
- D$\frac{3E_k}{4}$