# How to find wavelenght of a 3m spring with 2,5 Hz?

#### kontorstol

Hi! I just can't figure this out.

A 3m long spring makes transverse waves with a 2,5 Hz frequency. What is the wavelength?

I don't even know where to start, because in out incredible small physics course, we never learned this. :)

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#### valerioperi

Are these all the data you have? Does it say if the spring is fixed at its ends? Does it say if it's the fundamental armonic?

#### kontorstol

Thats all the info. The only formula have have learned is λ = v/f, and that won't work here after what I can see. There are four options after the question:

a) 0.67m
b) 3.75m
c) 1.5m
d) 6m

#### valerioperi

All right, then I think you have to assume that the spring is fixed at both its ends. Then you have a formula that states that only some particoular waves can occour in that spring (its armonics). Have you ever heard or seen this formula?

#### BvU

Homework Helper
Hello Konto, and welcome to PF. There must be more to this. Is there a preceding question that is continued in this one ?
If you can't find anything there, all I can advise is to look up (google) images of standing waves and see if you get some inspiration there....

#### Domenico94

you should check out other data that they gave you. This way, it's just impossible to understand. :)

#### kontorstol

First of all, sorry for not using the right template etc. when posting this topic. I will do better in future topics.

All right, then I think you have to assume that the spring is fixed at both its ends. Then you have a formula that states that only some particoular waves can occour in that spring (its armonics). Have you ever heard or seen this formula?
I have never heard about any other formula for finding wavelength than λ = v/f. We don't even have a book in physics, all the info we need is in a 75 page long compendium that the teacher made for the 6 week course, and the compendium never mentions such a formula.

Hello Konto, and welcome to PF. There must be more to this. Is there a preceding question that is continued in this one ?
If you can't find anything there, all I can advise is to look up (google) images of standing waves and see if you get some inspiration there....
This was the first question. :( I found a picture that was suppose to go with the question (didn't get printed). Maybe that can help?

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#### valerioperi

Yes the picture is extremely useful because tell us that the spring is fixed at its end and the wave is its fourth armonic. There are a lot of beautiful videos that could help you understandig what we are talking about: try searching on YouTube stationary waves.
The formula anyway says that $$\lambda = \frac{2L}{n}$$ where L is the length of the spring and n the number of the armonic.
It's an interesting stuff, expecially if you are interested in music, so I suggest you to try to understand it on your own, or even better ask your teacher for some useful sources :)

#### kontorstol

Well thats great news, thank you so much. :) Now I'll just have to ask the teacher why he would make a question that we never could figure out if we only look at the compendium. :)

#### BvU

Homework Helper
Looks as if you can now answer the question by just looking at the picture: how many wavelengths do you see ?

#### kontorstol

Looks as if you can now answer the question by just looking at the picture: how many wavelengths do you see ?
Wow, I did not realize that. :) Thanks for opening my eyes. :)

#### BvU

Homework Helper
Just to be sure I didn't wrong-foot you: what is your conclusion?

#### kontorstol

λ = 2*3m/4 = 1,5m :)

#### BvU

Homework Helper
Looks like the right answer to me !

"How to find wavelenght of a 3m spring with 2,5 Hz?"

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