Calculating Frequency of Standing Wave on a Fixed String | Physics Homework Help

[Workout]

I've never taken physics before and this is my first physics class in university.

Homework Statement

A string, 2.0 meters in length, is fixed at both ends and tightened until the wave
speed is 78 m/s. What is the frequency of the standing wave shown in the figure?

Homework Equations

v=nv/2L because it is fixed at both ends

The Attempt at a Solution

so f = (78m/s)/(2)(2)
and I get 19.5 Hz but that's not the right answer. It's too small. Help please?

 

[klawlor419]

It seems like there's some information missing in your outline of the problem. Perhaps try multiplying by an integer, n, that is the number of wavelengths the standing wave is comprised of.

 

[Workout]

Okay I actually just tried that. Here's the picture to the problem:

I thought the number of wavelengths was 6, but that doesn't seem to be right? Am I reading the picture wrong?

 

[klawlor419]

there's only 3 wavelengths in that picture;)

 

[Workout]

haha okay I see that now. So then I'd do

f = (78m/s)(3m)/(2m)(2)

and I'd get 58.5 which doesn't make sense. my answer either has to be A) 350Hz B) 230Hz C) 120Hz D) 470Hz and it's neither. so is my formula wrong maybe? because isn't frequency supposed to have units s? because that gives me units m/s.