WBJEE · Physics · Waves and Sound
A car is moving with a speed of \(72 \mathrm{km}\mathrm{h}^{-1}\) towards a roadside source that emits sound at a frequency of \(850 \mathrm{Hz}\). The car driver listens to the sound while approaching the source and again while moving away from the source after crossing it. If the velocity of sound is \(340 \mathrm{ms}^{-1}\), the difference of the two frequencies, the driver hears is
- A \(50 \mathrm{Hz}\)
- B \(85 \mathrm{Hz}\)
- C \(100 \mathrm{Hz}\)
- D \(150 \mathrm{Hz}\)
Answer & Solution
Correct Answer
(C) \(100 \mathrm{Hz}\)
Step-by-step Solution
Detailed explanation
By Doppler's Effect When observer is moving with velocity \(v_{0}\) towards a source at rest then approach frequency \[ N_{\text {Approach }}=N\left(\frac{v+v_{0}}{v}\right) \] where \(N=850 \mathrm{Hz}, v=340 \mathrm{ms}^{-1}, v_{0}=72 \mathrm{kmh}^{-1}\)…
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