Vibration and Frequency Questions

[Draco]

Homework Statement

A 75 g bungee cord has an equilibrium length of 1.20 m. The cord is stretched to a length of 1.80 m, then vibrated at 20 Hz. This produces a standing wave with two antinodes.

Homework Equations

Linear Density = m/L

The Attempt at a Solution

So far I've only found the linear density to be 0.0626kg/m. I'm stuck after this and have no clue on where to start next.

Homework Statement

Earthquakes are essentially sound waves traveling through the earth. They are called seismic waves. Because the Earth is solid, it can support both longitudinal and transverse seismic waves. These travel at different speeds. The speed of longitudinal waves, called P waves, is 8000m/s . Transverse waves, called S waves, travel at a slower 4500m/s . A seismograph records the two waves from a distant earthquake.

Homework Equations

Not sure.

The Attempt at a Solution

I'm not exactly sure on how to start this. This topic is very new to me. Can someone get me started?

 

[strikingleafs01]

So what I did for this question is, attempt to plug in values for 'm' so, for example

390 = m v/2L
390 = 1 343/2L

and find length that way,
it turned out that 390 represents the 3rd modal where (m = 3). Velocity is of course 343 m/s because sound will travel thorugh the tube which is open-open.

 

[Draco]

oh yeah, i got that question just after I posted. Thanks for explaining a different method though. I used a different way to find the length of the tube.

 

[Draco]

um can anyone fill me in on these two questions?