A block slides with speed \(v\) across a low-friction, horizontal surface and collides with and sticks to an identical block at rest. The combination then strikes a spring attached to a fixed wall, bouncing off elastically.

(a) Choose a system and discuss whether it is isolated.

(b) Sketch energy bar diagrams for the initial state, the state after the first collision, the state during the collision with the spring, and the state after the final collision.

(c) Discuss which types of internal energy are involved during this entire sequence of events.

(d) Determine the final speed of the combined blocks.