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Homework Help: Water waves problem

  1. Sep 6, 2009 #1
    1. The problem statement, all variables and given/known data
    The figure shows water waves traveling between two points P and Q, 20.0 cm apart. A dust particle on the water surface makes 5 complete oscillations in 2.0 s.

    What is :
    i. The amplitude;
    ii. The wavelength;
    iii. The frequency;
    iv. The speed of the waves ?

    2. Relevant equations
    [tex]v=\lambda f[/tex]

    3. The attempt at a solution
    i. amplitude = 4 cm

    ii. I don't understand the question. The question states that "A dust particle on the water surface makes 5 complete oscillations" and I think there should be 5 waves, but in the picture there are only 2.5 waves.
    The answer on the book is 8 cm. I guess it's from [tex]\lambda=\frac{20}{2.5}[/tex]

    But the answer for frequency is 2.5 Hz. I guess it's from [tex]f=\frac{5\;\text{waves}}{2\;s}[/tex]

    So I confused whether there are 2.5 waves or 5 waves.

  2. jcsd
  3. Sep 6, 2009 #2
    Re: wave

    the information "5 oscillations per 2 seconds" is not linked to the picture

    therefore the 8cm is correct, there are only 2.5 waves

    you wrote down the formula you need;

    v= lambda f

    therefore using the information as you quite rightly said the frequencey is 2.5 Hz, frequency is after all number of oscillations per second

    now you have the wavelength & frequency, the speed should be easy to work out
    Last edited: Sep 6, 2009
  4. Sep 6, 2009 #3
    Re: wave

    Hi Chewy0087

    Ah I get it now. The information "5 oscillations per 2 seconds" is not about the picture but it's still related to the question because we can't determine the frequency just based on the picture.

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