Minecraft wiki entry for Minecarts, associated text: Launching from rest via four powered rails, an occupied cart has enough momentum to climb a 1/1 slope 10 blocks high without further boosting and then travel horizontally at a very slow speed for at least a dozen blocks before coming to a stop. Such a cart does not have enough momentum to climb an 11 block high slope. An empty cart in a similar setup can climb only 5 blocks and then travel a few blocks horizontally.