We attach a ball of mass **m** to a rope of length **L**.
We hold the rope horizontal, above a frictionless floor.
On the floor is a box of mass **M**.

We release the rope. The ball swings down and strikes the box.
The ball bounces backwards at a final speed **v1**,
and the box slides forwards at a final speed **v2**.
The collision is ELASTIC.

What is the speed of the ball just before it strikes the box?
Call this speed **v0**.

What are the final speeds **v1** and **v2**?
Express them in terms of **v0, M, m**.