Ch 10.2 Quiz

Go down

Ch 10.2 Quiz

Post  Kathleen on Wed Nov 05, 2008 8:08 pm

1.) A car speeds away with 139.6 km/hrfrom a factory which emits a whistle sound at 1,318 Hz. What is the frequency registered by the driver of the car (see sheet 12,use 343 m/s for the speed of sound)? Indicate with a negative (positive) sign whether the frequency registered would be higher (lower) if the car moved toward the station

2.) You approach a wall while emitting sound at 326 Hz. The sound is reflected from the wall back at you and you register a reflected frequency of 551.5 Hz. What is your speed (see sheet 14,15,use 343 m/s for the speed of sound)?

3.) The length of a guitar string is 0.5817 m. What is the maximum wavelength of a standing wave on this string (see sheet 19) ? Indicate with a positive (negative) sign whether this is the only allowed wavelength (there are many other allowed wavelengths which are fractions of the wavelength you calculated).

4.) The traveling wave velocity on a string is 124.48 m/s and the longest wavelength of a standing wave on the string is 1.603 m. What is the frequency (see sheet 19) ? Indicate with a negative (positive) sign whether you calculated the minimum (maximum) frequency of a standing wave on this string.

Kathleen
Guest


Back to top Go down

Question 1

Post  Kathleen on Wed Nov 05, 2008 11:27 pm

Question 1:

Answer is NEGATIVE, because the closer you move to the station, the higher the frequency

You use the equation f' = ((v-v_o)/(v)) * f
There is a minus sign because the observer (v_o, the car) is receding and moving

Now with numbers

A car speeds away with 217.7 km/hrfrom a factory which emits a whistle sound at 1,401 Hz. What is the frequency registered by the driver of the car (see sheet 12,use 343 m/s for the speed of sound)?

FIRST, convert the km/hr to m/s by multiplying by 1000 m/km / 3600 s/hr
217.7 x (1000/3600) = 60.4722

f' = 343 - 60.4722 / 343 = .82369 * 1401 = 1153.998

Kathleen
Guest


Back to top Go down

Question 3

Post  ruipatel on Thu Nov 06, 2008 12:14 am

wavelenght/2 = L so rearrange it and you get 0.xxxm*2 (0.xxxx is whatever your meters are)

ruipatel
Guest


Back to top Go down

Question 3

Post  ruipatel on Thu Nov 06, 2008 12:17 am

The answer is NEGATIVE for question 3.

ruipatel
Guest


Back to top Go down

Re: Ch 10.2 Quiz

Post  Kathleen on Thu Nov 06, 2008 2:25 pm

Anyone figure out how to do 2 or 4 yet?
I've been trying to figure out 2 for some time now but can't seem to get it right.

I figured the equation would be something like f' = (v) / (v+vs) * f
Where vs is the source (you) and there is a + because you are approaching

I thought it might be
frequency registered = (343)/(343+vs) * frequency emitted
and then solve for vs but that doesn't seem to be right
Maybe we can all combine our methods on how we thought to do it to figure it out?

Kathleen
Guest


Back to top Go down

Question 2

Post  Kathleen on Thu Nov 06, 2008 4:22 pm

Okay so for #2, I'm not really sure why but you do

(frequency registered by you - frequency emitted) / (frequency registered by you + frequency emitted) = x

And then do X * frequency of sounds which is 343 m/s

You approach a wall while emitting sound at 344.3 Hz. The sound is reflected from the wall back at you and you register a reflected frequency of 541.1 Hz. What is your speed (use 343 m/s for speed of sound)?


So for example, it would be 541.1 - 344.2 / 541.1 + 344.2 = .2222 * 343 = 76.2394 m/s

Kathleen
Guest


Back to top Go down

question 4

Post  Guest17 on Thu Nov 06, 2008 4:37 pm

longest wavelength * 2 =L

F= 4*(velocity/(2*L))

Answer is negative

Guest17
Guest


Back to top Go down

?

Post  ? on Thu Nov 06, 2008 4:41 pm

that doesnt work for me for ques 4

?
Guest


Back to top Go down

Re: Ch 10.2 Quiz

Post  Guest17 on Thu Nov 06, 2008 4:53 pm

yeah i just realized it doesn't work for the maple ta but it gave me the right answer 2 times on the practice quiz

Guest17
Guest


Back to top Go down

Re: Ch 10.2 Quiz

Post  Guest17 on Thu Nov 06, 2008 5:00 pm

actually it does work i just typed in the number wrong the first time i did it on maple ta so that should work

Guest17
Guest


Back to top Go down

Re: Ch 10.2 Quiz

Post  Guest17 on Thu Nov 06, 2008 5:05 pm

here is the problem given worked out maybe this will help

1.603*2 = 3.206 =L

v/(2L)

124.48/ (2*3.206)= 19.41

19.41*4=77.65

Guest17
Guest


Back to top Go down

Re: Ch 10.2 Quiz

Post  confused on Thu Nov 06, 2008 7:00 pm

yes, thank you. see i multiplied the length by 2 for L, but then i didn't multiply it by two again under the division sign. Quick question though, why is it multipled by four though? Like, how did you know where to get that from?

confused
Guest


Back to top Go down

Re: Ch 10.2 Quiz

Post  guest17 on Thu Nov 06, 2008 7:20 pm

I have no idea I played around with it and I got the right answer when i multiplied it by four. the sheet says something about n being the number of wavelengths so i just started multiplying by each number until i got the answer because i wasn't sure how to find out how many wavelengths.

guest17
Guest


Back to top Go down

Re: Ch 10.2 Quiz

Post  abc on Thu Nov 06, 2008 8:14 pm

how about 3
any help?

abc
Guest


Back to top Go down

Q#3

Post  Elephant on Thu Nov 06, 2008 10:30 pm

#3 is simple,
just take the meters which is .5817 times it with 2 and that would be your answer (nagative answer)
.5817*2= (-)1.1634

hope this helps. so sleep tight now:)

Elephant
Guest


Back to top Go down

Re: Ch 10.2 Quiz

Post  Guesto on Fri Nov 07, 2008 1:05 am

I also didn't really understand that explanation for number two, so I did it this way...

f''=[(V+Vm)/(V-Vm)]f

The wall is both moving towards you as you are towards it. You can also convince yourself that because f'' is larger than f, you must add Vm on top and subtract Vm on the bottom so that the fraction will be greater than one. Then you just do some algebra and multiply it out. Both ways work...

Guesto
Guest


Back to top Go down

4 doesnt work

Post  yourmom on Fri Nov 07, 2008 4:05 am

4 didn't work for me =(

yourmom
Guest


Back to top Go down

#3

Post  super Mo on Fri Nov 07, 2008 7:28 am

The maximum wave length is already given to you in m. So it is simply v/length.
Do not multiply the length by anything, there is no need to.
answer in neg.

super Mo
Guest


Back to top Go down

Question 4

Post  heidy on Fri Nov 07, 2008 1:05 pm

i also tried number 4 a couple of times and it doesnt work for me either. I really don't understand why you multiply the fundamental by 4.

heidy
Guest


Back to top Go down

Question 4

Post  Heidy on Fri Nov 07, 2008 1:13 pm

Hey i just figured it out the question already states the longest wavelength and all you need to do is divide the velocity by the longest wavelength ( which is given) so it is simply: f=v/L

Heidy
Guest


Back to top Go down

Question #2

Post  DJ on Fri Nov 07, 2008 4:19 pm

Question 2:

You should have two numbers, one ~300, the other ~500. This example uses 303.1 Hz and 557.7 Hz. 343 m/s is the accepted speed.

x = (557.7-303.1)/(557.7 + 303.1) = 0.295771

Then,

v = xV = 0.295771 x 343 = 101.4495 m s^-1

DJ
Guest


Back to top Go down

Re: Ch 10.2 Quiz

Post  Sponsored content


Sponsored content


Back to top Go down

Back to top

- Similar topics

 
Permissions in this forum:
You cannot reply to topics in this forum