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Find the displacement.

  1. Apr 15, 2012 #1
    1. The problem statement, all variables and given/known data

    y=0.2msin[(0.18rad/m)x+(90 rad/s)t - pi/4]

    What is the displacement at position x=0 and t=0?

    2. Relevant equations

    y(x,t)=Asin(kx-wt+phi)

    3. The attempt at a solution

    y=0.2m[0.18-90]=-0.199m

    the answer is -.141 m help?
     
  2. jcsd
  3. Apr 15, 2012 #2

    Doc Al

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    Staff: Mentor

    Where did the 0.18 come from? x = 0.

    And don't mix radians and degrees. And don't forget the sine.
     
    Last edited: Apr 15, 2012
  4. Apr 15, 2012 #3
    As the above post said, the displacement is 0. This is because at x=0, t= 0, so everything in the sin function becomes 0. Sin of 0 is 0. Hence the displacement =0
     
  5. Apr 15, 2012 #4
    the displacement can't be 0 because the answer sheet says is -.141m and when i put x=0 i still get the same asnwer -0.199m don't get it.
     
  6. Apr 15, 2012 #5

    Doc Al

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    Staff: Mentor

    The value of x is 0, not the displacement (which is the y value).
    Show exactly what you did.
     
  7. Apr 15, 2012 #6
    Silly me, forgot the phase of the thing. Since everything else in the sin =0, then sin(-pi/4) =-1/(sqrt(2) multiply this by 0.2 and you get your answer of -0.141m.
     
  8. Apr 15, 2012 #7
    Never mind what i was doing was wrong i was subtracting .18-90 and the sine of that time 0.2m is .199m

    but what hypnosam is doing seems right

    I did y= 0.2sin[0.18(0)+90(0)-pi/4] but i just don't know how he got 0.707 when inmy calculator i get 0.013 for sin(-pi/4) wth.
     
  9. Apr 15, 2012 #8

    Doc Al

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    Staff: Mentor

    Make sure you're using radian mode.
     
  10. Apr 15, 2012 #9
    got it thanks!
     
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