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Wave amplitude problem

  1. Nov 9, 2004 #1
    A 4.0 Hz wave with an amplitude of 12 cm and a wavelength of 30.0 cm travels along a stretched string.

    (a) How far does the wave travel in a time interval of 3.0 s?

    (b) How far does a knot on the string travel in the same time interval?

    I got the answer to part (a) by using: x= lambda x (time/frequency)
    The answer I got for it was 3.6 m.
    I don't know what to do for part (b) Something to do with the amplitude, but I'm not sure...pls help! Thanks!
  2. jcsd
  3. Nov 9, 2004 #2
    Consider that a knot on the string reaches its amplitude peak four times each second. (also remember that a point on a string is not displaced horizontally when the string undergoes wave motion).
  4. Nov 9, 2004 #3
    ok....so, how would I figure (b) out? Since the amplitude is reached 4 times in a second, and the time interval is 3 seconds, and the amplitude is 12 cm, how would you figure out the distance traveled?
  5. Nov 10, 2004 #4
    Just a small refrase of your last message:

    you reach the amplitude of 12 cm 4 times per second for an interval of 3 seconds...

    This might enable you to see the answer...

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