Because if the one falling 20ft lands on a seesaw, the other side of it will toss two balls each of the same mass 10ft up.
Then 20ft should not be used in the explanation. They should just have one ball going at 2x speed hit the seesaw and have 4 of those balls go up at 1x speed.
alt Hacker News
Then 20ft should not be used in the explanation. They should just have one ball going at 2x speed hit the seesaw and have 4 of those balls go up at 1x speed.