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Homework Help: Tension of a cable as a result of a pulse (wave)?

  1. Jan 17, 2012 #1
    1. The problem statement, all variables and given/known data

    A ski gondola is connected to the top of a hill by a steel cable of length 620 m and diamter 1.5 cm. As the gondola comes to the end of its run, it bumps into the terminal and sends a wave pulse along the cable. It is observed that it took 16 s for the pulse to return.

    (a) What is the speed of the pulse
    (b)What is the tension in the cable?

    2. Relevant equations

    simple velocity equation: v = d/t
    density equation: p = m/v
    speed of wave on a cord: v = √[(F)/(m/L)]

    3. The attempt at a solution

    I was sucessful with part a of the question. It's just a simple velocity equation: v = 620/16 = 38.75 s.

    For the second part, I know I need to find mass, so I could plug it in the speed of wave in a cable equation. I tried to use the simple density equation since I already have information for the cross-sectional part of the cable:
    m = pv
    m= p (LA)→length times area
    m = ???

    It seems I don't have enough information to find mass because I don't have p (density)!
    Last edited: Jan 17, 2012
  2. jcsd
  3. Jan 18, 2012 #2
    You can find the density of steel online. It ranges from 77500 to 80500 kg/m3 depending on alloy
  4. Jan 19, 2012 #3


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Many physics textbooks have a table of densities for different materials. It would be in the section of the chapter that discusses density. They probably expect you to use the value from such a table -- rather than finding it on the web, which would have some variability since there are actually different types of steel with different densities.
  5. Jan 22, 2012 #4
    Thanks, it never came across my mind that density was a given value! I will check my textbook.
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