HOMEWORK FROM THE BOOK
(starred problems have answers provided)

CHAPTER 13 PROBLEMS- 40, 43*, 45, 51
CHAPTER 14 PROBLEMS- 1*,2, 3, 7, 49, 50*, 51, 61*, 75
CHAPTER 21 PROBLEMS- 58, 59
 

Chapter 13

43. A piano emits frequencies that range from a  a low of about 28 Hz to a  high of about 4200 Hz, Find the range of wavelength spanned by this instrument. The speed of sound in air is approximately 343 m/s.

v=f(wavelength)
(343m/s)/28Hz=12.25nm

(343m/s)/4200=.082nm

Range of wavelength for the instrument is: 0.82nm to 12.25nm
******ALWAYS INCLUDE YOUR UNITS******

Chapter 14

A sound wave has a frequency of 700Hz in air and a wavelength of 0.50m. What is temperature of air?

v= wavelength (f)
700hz(0.50m)=350 m/s

Now take that information and plug it into this equation...

v=931(m/s) [Square root1+T/273]
350m/s=(331m/s)[sq.root.1=T/273}

T=32C
 

50. A 50m long brass pipe open at both ends has a fundamental frequency of 350Hz. a) Determine the temperature of air in the pipe. b) If the temperature is increased by 20C what is the new fundamental frequency of the pipe? Be sure to include the effects of temperature on both the speed of sound in air and the length of the pipe.

We'll help you out with this one, but no answers...

a) Temp? First....remember the equation Mr. Williams gave you on that worksheet with all those drawings of waves??
Here it is to refresh your memory...
331+.6T=v
              Plug in all the numbers (you must solve for velocity)

b) Now that you have the temperature use the same equation, but increase the temp. by 20C.
 

61.  A commuter train passes a passenger platform at a constant speed of 40m/s. The train horn is sounded at a frequency of 320 Hz when the train is at rest. a) What is the frequency observed by a person on the platform as the train approaches and b) as the train recedes from him? C) What wavelength does the observer find in each case?

For a and b us the equation:
f heard=f emitted Vw(+or-)Vobserver/Vv(+or-)Vsource

For part c you know the velocity and frequency....now brainstorm for that simple formula....if you don't remember v=wavelength (frequency) by now, you are in trouble!