When minecarts derail on descending slopes they lose a chunk of their horizontal momentum and all of their vertical momentum. This is in stark contrast to ascending slopes which work perfectly fine.

The loss of horizontal momentum is more visible at default speed (maxSpeed 8) and the loss of vertical momentum is more visible on high speed (maxSpeed 1000)

1. Nonsensical trajectory resulting from the incorrect momentum (maxSpeed 1000)

2. Example of losing horizontal momentum:
downward.mp4
3. Results of a downward vs upward derailing at maxSpeed 8 (both should be the same since they had the same horizontal momentum, but that's not what's observed)

4. Here you can see me lose all my vertical momentum and go perfectly horizontally for a while before gravity starts acting.
downward fast.mp4

Reproduction Steps

• Reproduction world: Bug Repo.zip
• Drive onto the downward and upward ramps
• Compare results
• Set maxSpeed to 1000
• Drive off the downwards ramp

Observed Results

• The minecart going downwards loses some horizontal momentum
• The minecart going downwards loses all vertical momentum

Expected Results

• The minecart would keep its momentum realistically like it does on ascending slopes.