The tension in a 2.6-m-long, 1.1-cm-diameter steel cable (ρ = 7800 kg/m3) is 860 N. What is the fundamental frequency of vibration of the cable?

The answer is 6.55 Hz.

I know that I'm going to use the formula:
f=nsqrt(T/4L^2u)
However, I'm not sure how to get the u for this equation. Any help is appreciated.

2 answers

You need to find the mass of the cable and divide it by the length to get the mass per unit length.
Volume of cable = pi r^2 L
Mass of cable = pi r^2 L * 2.6
so
mass/length = 7800 * pi * (.011)^2
Thank you! I was able to figure out the correct answer. However, in this case shouldn't (.011^2) be (.011/2)^2?