# Homework Help: 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.