Physics help

[jmcoreymv]

Im studying for my midterm and im trying to figure out how to do this problem:

Suppose two loudspeakers are separated by three meters and are being driven by exactly the same sinusoidal signal at a frequency that can be varied. If you are located four meters away directly in front of one of the speakers, determine the three lowest frequencies for which you would hear constructive interference. (assume temp is 25 C)

I know the speed of sound in air is v=331*sqrt(T/273) where T is in Kelvin. But Im not sure where to go from there.

 

[LordMorpheus]

ok, its been a while, but I think I can help.

You got two speakers. You are 4 meters from one, and 5 from the other (sqrt(3^2 + 4^2))

the difference in the distances is obviously 1 meter.

In order to hear constructive interference, the wavelength MUST BE an even multiple of one (i.e: 1 meter, .5 meter, .333 meter, .25 meter, etc.)

So, for the lowest frequency (highest wavelength) the wavelengths will be 1 meter, half a meter and one third of a meter.

You can do the rest.

if that speed equation of ours is right (don't remember it) you get:
345.8Hz
691.6Hz
1037Hz

 

[bleeb]

Remember that F=ma=m(dv/dt)=m(d^2x,dt^2). That should help you out. Remember the properties of waves too.

 

[LordMorpheus]

Originally posted by: bleeb
Remember that F=ma=m(dv/dt)=m(d^2x,dt^2). That should help you out. Remember the properties of waves too.

there is no calculus required . . .. Why are you trying to make his head hurt? You enjoy doing it, don't you?

 

[jmcoreymv]

Thanks! I sort of had an idea about how to go ahead and do it but I couldnt nail it down.

 

[bleeb]

Originally posted by: LordMorpheus

Originally posted by: bleeb
Remember that F=ma=m(dv/dt)=m(d^2x,dt^2). That should help you out. Remember the properties of waves too.

there is no calculus required . . .. Why are you trying to make his head hurt? You enjoy doing it, don't you?

heheh just giving some good advice. I recall where I was stuck on a few physics problems back in college and after a good night sleep, that equation came into my head and thus the solution to the problem. =)