Two speakers are driven by the same oscillator with frequency of 140 Hz. They are located 4.00 m apart on a vertical pole. A man walks straight toward the lower speaker in a direction perpendicular to the pole. He will hear the minimum in sound intensity twice.

Question

Two speakers are driven by the same oscillator with frequency of 140 Hz. They are located 4.00  m apart on a vertical pole. A man walks straight toward the lower speaker in a direction perpendicular to the pole.  He will hear the minimum in sound intensity twice.
How far is he from the pole at these moments?

Damon · Answer

When is the difference in distances equal to half a wavelength or 1.5 wavelengths?

Look up velocity of sound call it c
then period = 1/f = L/c where L is wavelength
Calculate L from that

say man is x meters from pole
distance to lower speaker is x
distance from higher speaker is
sqrt (x^2+4^2)
difference = sqrt(x^2+4^2) - x
when is that equal to L/2 ??