Tension of a cable as a result of a pulse (wave)?

1. Jan 17, 2012

LastXdeth

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. Jan 18, 2012

RTW69

You can find the density of steel online. It ranges from 77500 to 80500 kg/m3 depending on alloy

3. Jan 19, 2012

Redbelly98

Staff Emeritus
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.

4. Jan 22, 2012

LastXdeth

Thanks, it never came across my mind that density was a given value! I will check my textbook.

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