Problem C7:
A horn, which is stationary on the ground, is producing sound with a frequency n_{1} Hz. You are
driving your car with a speed of v/n_{2}, where v is the speed
of sound in air. See the figure below. If n_{2} is positive,
you are driving away from the horn, and if n_{2} is negative you
are driving towards the horn. What is the frequency of the horn's sound
that you hear? If you hear a frequency of n_{3} Hz,
what is n_{3}? Note that n_{1} and n_{3} have units of
Hz, and n_{2} is unitless.

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