Concept:This is a classic Doppler effect problem where a sound source approaches a stationary observer.
Formula:$$ f' = \left( \frac{v}{v - v_s} \right) f $$
Solution:- Assume standard velocity of sound in air \( v \approx 330 \text{ m/s} \).
- Source velocity \( v_s = 33 \text{ m/s} \) and true frequency \( f = 450 \text{ Hz} \).
- Substitute into the formula: \( f' = \left( \frac{330}{330 - 33} \right) 450 \).
- Calculate the denominator: \( 330 - 33 = 297 \).
- Simplify the fraction: \( \frac{330}{297} = \frac{10}{9} \).
- Multiply by the base frequency: \( f' = \frac{10}{9} \times 450 = 10 \times 50 = 500 \text{ Hz} \).
Why other options are incorrect:Option B would be correct if the source were receding (moving away). Option D is the original frequency, incorrectly assuming no Doppler shift occurs.
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