On February 01 2006 17:22 Ack1027 wrote:
K so I'm just gonna say ahead of time that this is my physics hw and hope I don't get bashed. If you can find the room in your hearts to help me cuz I definitely don't know how to do these physics problems, I would really appreciate it.
The average sound intensity inside a busy restaurant is 3.4 10-5 W/m2. How much energy goes into each ear (area = 2.1 10-3 m2) during a 2-hour meal?
do you mean 2.1*10^-3? and i've never heard of some value referred to as "sound intensity."
A string of length 2.7 m is fixed at both ends. When the string vibrates at a frequency of 80.0 Hz, a standing wave with 6 loops is formed.
(a) What is the wavelength of the waves that travel on the string?
m
(b) What is the speed of the waves?
m/s
(c) What would be the fundamental frequency of this string?
Hz
this isn't too hard, physics generally (i'm assuming you're taking AP Physics, it sounds a lot like it) runs on finding an equation which fits all the givens but one, which you continue solving for a single variable until you have what you need. in this case, the fact that 6 loops are formed means that the wave is travelling at its 6th natural frequency n (or something, it has been a while). i know for a fact your book should have some sort of equation that looks like this:
f = n*sqrt(lambda/Length), where lambda is wavelength. that's not the exact equation i'm sure, but look for something like that, it should work out.
When a tuning fork is sounded together with a 489-Hz tone, a beat frequency of 2 Hz is heard. Then a small piece of putty is stuck to the tuning fork, and the tuning fork is again sounded along with the 489-Hz tone. The beat frequency decreases. What is the frequency of the tuning fork?
beats are heard when there is a discrepancy in frequency; a discrepancy of x Hz means that the two frequencies are x Hz apart (hard stuff, aint it). in this case, since the beat frequency is 2, that means the tuning fork is either 2 Hz above or below the 489 Hz tone. Putting a piece of putty to a tuning fork should reduce its frequency, meaning that when the beat frequency heard by the observer is reduced, that means that the discrepancies in frequency is reduced as well.
you should be able to figure out what the frequency of the tuning fork is now