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A string is stretched between fixed points separated by 75.0 cm. It is observed to have resonant frequencies of 420 Hz and 315 Hz. There are no other resonant frequencies between these two. Then, the lowest resonant frequency of this string is

1. 105 Hz
2. 1.05 Hz
3. 1050 Hz
4. 10.5 Hz

Correct answer: 105 Hz

Solution

Consecutive resonant frequencies of a fixed string differ by the fundamental: f0 = 420 - 315 = 105 Hz, which is the lowest resonant frequency.

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