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Help with wave speed

  1. May 24, 2010 #1
    1. The problem statement, all variables and given/known data
    A block of mass 3.1 kg rests on a frictionless inclined plane, held in place by a string of mass 0.023 kg. The angle of the plane from the horizontal is 32°, and the string length is 1.5 m. How long does it take a wave to travel from one end of the string to the other? Note: Since the string is so much less massive than the block, the mass of the string can be neglected when calculating its tension.

    2. Relevant equations
    v= square root of F/linear density
    v= Distance/Time



    3. The attempt at a solution


    I have worked this several times and I keep coming up with .025. I got force of gravity in the x direction and came up with 55.1N. I then divided that by the linear density (.023/1.5m.) After taking the square root of that, my V was 59.9 M/s. I then put that in the V= D/T and got .025. Please tell me where I'm going wrong here. Thanks!
     
    Last edited: May 24, 2010
  2. jcsd
  3. May 24, 2010 #2

    Doc Al

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    Staff: Mentor

    Show how you got that.
     
  4. May 24, 2010 #3
    30.38/sin32
     
  5. May 24, 2010 #4

    Doc Al

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    Staff: Mentor

    That's incorrect. You need to review how to find the component of weight parallel to the incline.
     
  6. May 24, 2010 #5
    ahhh i knew it would be something stupid like that! Ill look into it and get back on here. Thanks
     
  7. May 24, 2010 #6
    Hmm still confused. I think im getting the angles in the wrong places. Is it Fgx= 30.38/cos32?

    Edit

    I dont think thats right. . . i dont know where I'm going wrong
     
  8. May 24, 2010 #7
  9. May 25, 2010 #8
    Figured it out. Thanks for the help
     
  10. May 25, 2010 #9

    Doc Al

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    Staff: Mentor

    I'm glad you figured it out. In your diagram, you have the x-component as the hypotenuse of your right triangle. That's incorrect. The hypotenuse is always the full vector, which in this case is Fg; the components are the smaller sides.
     
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