In the diagram, there are two identical spheres X and Y. At first, X travels at speed $v$ straight towards Y, while Y is at rest. The spheres then undergo an elastic collision. What occurs?
- AX moves with speed $\frac{1}{2}v$ to the right; Y moves with speed $\frac{1}{2}v$ to the right
- BX moves with speed $v$ to the left; Y remains stationary
- CX moves with speed $\frac{1}{2}v$ to the left; Y moves with speed $\frac{1}{2}v$ to the right
- DX stops; Y moves with speed $v$ to the right