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Displacement of a wave

  1. Apr 21, 2014 #1

    I don't understand why I keep getting a negative result...

    1. The problem statement, all variables and given/known data

    The displacement (in metres) of a wave is given according to

    y = 0.26 sin(πt − 3.7πx),

    where t is in seconds and x is in metres,

    What is the displacement y when t = 38 and x = 13 [m] ?

    2. Relevant equations

    3. The attempt at a solution

    The wave travels in the +x direction because as time increases so does the displacement, so i'm expecting a +ve result.

    [itex]y = 0.26 \sin (\pi 38 - 3.7 \pi 13)[/itex]

    This keeps giving me [itex] y = -0.1367[/itex] as an answer which surely can't be correct.

    I don't know what i'm doing wrong...


  2. jcsd
  3. Apr 21, 2014 #2


    User Avatar
    Science Advisor

    You seem to be misunderstanding the word "displacement". A wave moves up and down as it travels. It is, as you have calculated, the y coordinate, not movement in the x direction. It certainly can be negative.
  4. Apr 21, 2014 #3
    You're right, I had misunderstood that - Thanks, it makes more sense now.

    I also did the calculation in degrees which explains why the magnitude of my answer was wrong.
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