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Homework Help: Sin waves

  1. Apr 15, 2010 #1
    1. The problem statement, all variables and given/known data

    Transverse waves on a string have wave speed 8.00 {\rm m/s}, amplitude 0.0700 {\rm m}, and wavelength 0.320 {\rm m}. These waves travel in the x direction, and at t = 0 the x = 0 end of the string is at y = 0 and moving downward.

    Find the frequency of these waves: (found: 25.0 Hz)
    Find the period of these waves. (found: 4.00 E-2 s)
    Write the equation for {y}({x},\:{t}) describing these waves. (Stuck).
    Find the transverse displacement of a point on the string at x2 = 0.160 m at time t2= 8.50×10−2 s. (Stuck).

    2. Relevant equations

    3. The attempt at a solution
    For the third part, this is what I have so far: .07(sin 0)
    I don't know if its right. I'm thinking I can probably get the next part if I know what the equation is. Any help? Thanks!
  2. jcsd
  3. Apr 15, 2010 #2


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    Do you know the equation for a wave propagating down a string?

    y=Asin(kx-wt) what values for A, k, and w would make this work?
  4. Apr 15, 2010 #3
    K= I'm not sure, but wouldnt x be zero so k would cancel out?
    W= i don't know how to go about finding.
  5. Apr 15, 2010 #4


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    Think about what the equation is saying.

    At t=0, the equation says: y=Asin(kx)

    So, can you see from there what k should be? Hint: Think about what a wave looks like on that string, and what the y coordinate is for each x coordinate.

    Similarly, think at x=0 the equation says y=Asin(wt). what does that say?
  6. Apr 15, 2010 #5
    I don't know :/.. is there any other way you could explain it? I'm sorry, it's late and I feel so slow!
  7. Apr 15, 2010 #6
    Oh! So I've gotten .07sin(157t-19.6x), but it's telling me it's wrong.??
  8. Apr 15, 2010 #7
    Nevermind, got it, thanks!
  9. Apr 15, 2010 #8


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    no problem =)
  10. Apr 15, 2010 #9
    Oh, another question.. for the last part, I'm just plugging and chugging in the numbers to the equation .07sin(-157t+19.6x), and I'm getting -.0124. It says it's wrong. Am i doing something wrong?
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