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: Waves velocity

  1. Mar 3, 2009 #1
    1. The problem statement, all variables and given/known data

    the question is:the floats of 2 men fishing in a lake from boats is 21m apart.the waves causes both boats to bob up-down 20 times/minute.A third man observes that one of his colleagues is on the crest while other is on trough,and there is a one crest distance between them?find velocity

    2. Relevant equations

    v=f(lambda)

    3. The attempt at a solution
    idk but would f=20 and lambda=which i cant figure out1/4 or something
    help pls
    =(
     
  2. jcsd
  3. Mar 3, 2009 #2

    Delphi51

    User Avatar
    Homework Helper

    In order to use your v = f*lambda formula you need to know the wavelength, and it is not at all clear from the wording of the question. It looks like the wording has been messed up - can you check and make sure it is copied word for word? In particular, I don't understand "one crest distance" and are they saying the boats are 21 m apart or the floats are 21 m apart?
     
  4. Mar 3, 2009 #3
    k here is the actual question format:The floats of two men fishing in a lake from boats are 21m apart.The waves causes boats to bob up and down 20 times per minute.A man in a third boat observes that when the boat of one of his colleagues is on the crest of a wave,that of the other is in a trough,and that there is one crest between them.what is Velocity.
     
  5. Mar 3, 2009 #4

    Delphi51

    User Avatar
    Homework Helper

    Much better! The boats are 21 m apart and they are 1.5 wavelengths apart. From that you can calculate the wavelength. Careful with the units - remember the frequency is per MINUTE.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook