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Homework Help: Velocity and displacement question

  1. Sep 21, 2005 #1
    Swimming at 0.15 m/s relative to still water, a swimmer heads directly across a 100-m-wide river. He arrives 50 m downstream from a point directly across the river from his starting point.
    a) What is the speed of the current in the river?
    b) In what direction should the swimmer head so as to arrive at a point directly opposite his starting point?

    I got 13.3 meters/second for part (a). Can someone check this?
    For part (b), I am unsure of what to do. Can someone give me a hint in the right direction?
  2. jcsd
  3. Sep 21, 2005 #2
    For part b: If the swimmer wanted to stay in one place, how fast would he have to swim? In what direction? Hopefully, this speed is less than the swimmer's stop speed, otherwise there'd be no way he could swim across without being swept downstream. This leads me to believe your answer for part a of 13.3 m/s is incorrect. Besides, 13.3 m/s is a very fast speed for a river.
  4. Sep 21, 2005 #3
    Your answer for (a) is correct, for b, try using a vector approach.
  5. Sep 21, 2005 #4
    (a) can't possibly be correct. If there were no current, the swimmer would cross the river in 100/0.15 = about 600 seconds. In the same time, a current of 13.3 meters/s would sweep the guy 8000 meters downstream.
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