Question 126076: After leaving the boathouse, a rower rowing upstream passes a log 2 km upstream from the boathouse. The rower rows upstream for one more hour and then rows back to the boathouse, arriving at the same time as the log. How fast was the current flowing?
Answer by Edwin McCravy(20060)   (Show Source):
You can put this solution on YOUR website! After leaving the boathouse, a rower rowing upstream passes a log 2 km upstream from the boathouse. The rower rows upstream for one more hour and then rows
back to the boathouse, arriving at the same time as the log. How fast was the
current flowing?
It's easy if you can do some bizarre thinking, imagining and pretending.
Pretend that the river is still (I said it takes bizarre thinking!) and that the
land with the boathouse is moving at the same rate at which we normally say the
river is flowing. Then the log is not moving at all. The rower goes up a
certain distance for an hour and back at the same rate (relative to this
imagined still river). That takes two hours. Meanwhile the boathouse has moved
up to the log. So since the boathouse takes two hours to move up the 2 km to
the log, the boathouse moves 1 km/hr.
The rate of the current is the same as the rate we were pretending that the
boathouse is moving alongside the "still river". So the answer is 1 km/hr.
Edwin
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