Minecraft wiki entry for Minecarts, associated text: When traveling up a slope at full speed (8 m/s) one powered rail is sufficient to maintain full speed for two blocks high, meaning that alternating between powered and unpowered rails maintains full speed up a slope. Consecutive powered rails on a slope adds more momentum, so eight powered rails can be followed by 8 normal rails to maintain full speed while traveling up the slope. Less momentum is gained by each consecutive rail as the strip gets longer.