Question about a swimmer crossing a river:
My book says that if a swimmer wants to cross a river in the shortest time, her velocity relative to the WATER will be straight ahead... I know this question is all about POV, but I am bit confused... Wouldn't her velocity relative to the GROUND be straight ahead, and her velocity relative to the water be at some angle upstream?

Question

Question about a swimmer crossing a river: 
My book says that if a swimmer wants to cross a river in the shortest time, her velocity relative to the WATER will be straight ahead... I know this question is all about POV, but I am bit confused... Wouldn't her velocity relative to the GROUND be straight ahead, and her velocity relative to the water be at some angle upstream?

anonymous · Answer

The difference is whether she is trying to go from point A to point B, in which case, you are right, she should swim a bit against the flow. "Cross the river" meaning just "get to the other side, somewhere" means going at right angles to the flow to get through the flow as fast as possible.

anonymous · Answer

Ooooooh.... nice, thank you.