[BerntR]

Hello Jeff,

Since there is friction here, A is doing work even though the speed becomes constant after a while.

If B's contribution is only to turn a linear movement into a circular movement, B is not doing any work. The object is always moving perpendicular to the direction B is pushing. The angle between the object movement and B's pull force need to be different from 90* before any work is done. Changing direction is not the same as doing work - even though it makes a significant difference.