Beat Frequency/Truck Speed!

ravenprp

Two loudspeakers emit 300 Hz notes. One speaker sits on the ground. The other speaker is in the back of a pickup truck. You hear 9.00 beats per second as the truck drives away from you.

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Alright, I'm assuming this problem has to deal with doppler shifts + beat frequency.

The observer is stationary (the guy) as the source moves away. Therefore am I to believe that F_observer = F_source * (v_w / v_w + v_s) where v_w is 343m/s, F_source = 300 Hz,

Now for beat frequency, I know that is F_beat = F_1 - F_2 = 9 beats/sec -- so does that mean

F_observer = 291 Hz?? I'm not sure because 300Mhz - 9 = 291?

I am almost 80% sure I'm wrong, but this feels like a doppler shift question to me. Am I on the right track, at least?

Thanks all

Btw, how do I input LaTex commands in here? Do I type the code?

\int

ravenprp

I need help, I still can't figure this out! Anyone?