Bob is having a nice camping/fishing trip along a river. He leaves his campsite early in the morning, and gets on his boat, heading full throttle upstream.

After going for exactly one mile, his hat flips off of his head, and starts floating downstream. Bob doesn't realize that his hat has fallen off for five minutes, but then he notices that it's missing, and turns full throttle downstream.

He finally catches the hat at exactly the same spot as he camped that morning. The question is, how fast was the water traveling?

(Assume that he travels the same speed the entire time and that there is no turn around time.)

Since time difference is independent of frame of reference, in the f.o.r. of the river the hat is stationary while Bob is moving with a constant velocity.
So the time taken by Bob to recover his hat will be twice that taken for maximum separation with it.
Total time taken to recover the hat = 2 * 5mins.
= 10 minutes
As the hat covers a distance of 1 mile in this time interval the river velocity will be .1 mile/min.

Posted by spinoza on 2003-05-08 00:56:08