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How to find wavelength of wave?

  1. Oct 8, 2015 #1
    1. The problem statement, all variables and given/known data
    A backyard pool is 14.5 m long. For fun Sally uses a board to create waves. Sally investigates the effect these waves have on Susan who is floating on another board near the middle of the pool. Sally notices that the waves travel with a speed 6.2 m/s.

    a) If Sally moves the board up and down (ie. through one complete oscillation) every 0.64s what wavelength does Susan observe?

    b) Sally sets up a standing wave with four peaks along the length of the pool (there is no movement at the two ends of the pool). The wave speed remains the same, what period is Sally moving the board with now?

    2. Relevant equations
    f = 1/T
    λ = v/f

    3. The attempt at a solution
    a) λ = v/ 1/T
    = 6.2 1/0.64
    = 3.968 m (which is correct)
    b) Four peaks would mean λ = 3.968 x 4
    = 15.872 m
    f = 1/T, then T = 1/f
    v = fλ and f = v/λ
    then T = 1/ v/λ
    so, T = 1/ 6.2/15.872
    = 2.56s

    Would this be correct? Thank you
  2. jcsd
  3. Oct 8, 2015 #2


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    Gold Member

    ..but pool is only 14.5m long. Try drawing the pool and standing wave as described.... "four peaks along the length of the pool (there is no movement at the two ends of the pool)"
  4. Oct 8, 2015 #3
    Does that mean λ = 14.5m?
  5. Oct 8, 2015 #4


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    Homework Helper

    No. That would mean only one peak.
  6. Oct 8, 2015 #5
    What does one wavelength look like? A diagram may help shed some light.
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