A sailboat race is held on a river that runs directly North to South, with a current of 12 knots. A 25 mile race is held going downriver (south). The first heat is held early in the day when there is no wind. The second heat, also going downriver, is held later, when there is a 12 knot tailwind (from the North). In which heat are the fastest times recorded?

(In reply to re: solution by Joel)

I also find tacking counterintuitive. But in still water, with the wind coming directly from the south, it is possible to proceed southward on a zigzag path by tacking. The first heat represents this condition, though it happens that the dry land is, relatively speaking, going northward along with the wind, so the relative speed of the boat vis-a-vis the land is the 12 knots the land is travelling plus whatever counterintuitive progress the boat is making in the water.  In the second heat the relative motion of the boat to the land is only the 12 knots.

Posted by Charlie on 2007-02-14 10:06:57