1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Swimmer in River

  1. Apr 8, 2005 #1
    Q. A river 590 ft wide flows with a speed of 6 ft/s with respect to the earth. A woman swims with a speed of 3 ft/s with respect to the water.
    a) If the woman heads directly across the river, how far downstream is she swept when she reaches the opposite bank?
    d1 = ft *
    1179.96 OK

    b) If she wants to be swept a smaller distance downstream, she heads a bit upstream. If she heads 29° upstream, how far downstream is she swept before reaching the opposite bank?
    d2 = ft

    Any ideas on part b

    c) For the conditions of part (b), how long does it take for her to reach the opposite bank?
    Any ideas on part c

    Please help me !!!
  2. jcsd
  3. Apr 8, 2005 #2
    Aha I remember this from vectors in grade 10.

    Remember relative velocity law:

    V woman,earth = V woman,water + V water,earth

    Draw your diagrams, look at the components, add them. find scalar multiple k so that the vertical component is 590 (the width of river) and the horizontal component is how far she is swept downstream. k is the time it takes to get the the other side.

    Part b: exactly the same as part a, except change your vectors so she heads 29 degrees instead of being perpendicular to the current of the river.

    Part c: same as part a; find k a scalar multiple such that the vertical component is the width of the river. k is the time it takes.

    By the way it's so funny seeing things in feet and feet per second. I kind of gained an impression about how annoying it must be for poor americans learning science and having been brought up to know the old-fashioned units and not metric!!
  4. Apr 9, 2005 #3
    Here is what I did for part b,

    d = v0 cos theta * t

    width of the river, d = 590 m

    velocity of the river = 6ft /s

    velocity of the woman = 3ft/s

    so, t = d / vwoman * cos (29)

    t= 590 /3 * cos(29)

    After finding t , we can multiply this t with 6 ,which is the velocity of the river.

    I doubt if this right, but please help!
  5. Apr 11, 2005 #4
    No luck with this problem for the last 2 parts, can anybody tell me if something is wrong here.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook