Simple standing wave question- not exactly sure why I can't get answer?

[~christina~]

[SOLVED] simple standing wave question- not exactly sure why I can't get answer?!

Homework Statement

A particle fingering flute sounds note with frequency of 880Hz at 20 deg celcius(343m/s => sound wave speed) The flute is open at both ends.

a) find the air column length

b) find the frequency the flute produces at beginning of football game when ambient temp is -50.0C and muscician has not had time to warm up flute.

answers supposed to be=> a) 0.195m and b) 841m

Homework Equations

$$f= n\frac{v} {2L}$$

$$v= f*\lambda$$

The Attempt at a Solution

a) find the air column length

I really did try to do this and what I did was I got
v= 343m/s
f= 800Hz

$$342.91m/s= 800Hz \lambda$$
$$\lambda= 2L$$
L= 0.206875m=> not the answer in the book?!

b) find the frequency the flute produces at beginning of football game when ambient temp is -50.0C and muscician has not had time to warm up flute.
$$v= 331 \sqrt(1 + 20^oC/273^oC)= 299.1567m/s$$
based on L before:
L= 0.206875m

$$f= v\lambda= 288.15e69/0.41375= 723.0378$$=> why isnt' this matching the book answer??

Please help...
it's really a simple problem I think.

THANK YOU

 

[tiny-tim]

A particle fingering flute …

A what?? … is it electron-ic? …

… sounds note with frequency of 880Hz at 20 deg celcius(343m/s => sound wave speed) The flute is open at both ends.

I really did try to do this and what I did was I got
v= 343m/s
f= 800Hz

$$342.91m/s= 800Hz \lambda$$
$$\lambda= 2L$$
L= 0.206875m=> not the answer in the book?

Hi christina!

You've used 800 instead of 880 - does that help?

 

[~christina~]

A what?? … is it electron-ic? …

um no, I don't think so since they don't say anything about that.

Hi christina!

You've used 800 instead of 880 - does that help?

yes that helps for the first part but I can't figure out what's wrong with the second part...I plugged in the number (found in a)to find the wavelength but then it came out ot 767Hz for the frequency. I can't figure out what's wrong with the second part.

b) find the frequency the flute produces at beginning of football game when ambient temp is -50.0C and muscician has not had time to warm up flute.
$$v= 331 \sqrt(1 + 20^oC/273^oC)= 299.1567m/s$$
based on L before (corrected):
$$\lambda= 0.389670m$$

$$f= v\lambda= 288.15e69/0.389670$$= 767.717Hz[/tex]

Thanks tiny-tim

 

[tiny-tim]

b) find the frequency the flute produces at beginning of football game when ambient temp is -50.0C and muscician has not had time to warm up flute.
$$v= 331 \sqrt(1 + 20^oC/273^oC)= 299.1567m/s$$
based on L before (corrected):
$$\lambda= 0.389670m$$

$$f= v\lambda= 288.15e69/0.389670$$= 767.717Hz[/tex]

Hi!

I don't follow any of this.

Where does the difference between -50º and +20º come in?

(btw, do you Americans really play football at -50ºC?)

 

[~christina~]

Hi!

I don't follow any of this.

Where does the difference between -50º and +20º come in?

(btw, do you Americans really play football at -50ºC?)

Um...they say that the temperature is -50º so wouldn't that play a part here because if that didn't matter wouldnt' the frequency be the same as in the original question?

I don't know about football though.

 

[~christina~]

I found out that the temperature was -5C not -50C so that's what was wrong...slaps forehead*

Thanks for your help tiny-tim.

 

[Hootenanny]

I believe that your using the wrong equation, or at least plugging the wrong numbers in. See http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html" for more information.

 

[~christina~]

I believe that your using the wrong equation, or at least plugging the wrong numbers in. See http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html" for more information.

I was plugging in the wrong number for the temp (-5(right) vs -50 (wrong number))