Coming Sound

Classical Mechanics Level 2

A sound source with frequency 100 100 Hz is approaching Calvin with a speed of 20 20 m/s , while Calvin riding a bicycle toward the sound source with a speed of 60 60 m/s, as above. If the speed of the sound wave is 340 340 m/s, what is the frequency of the sound that Calvin hears?

200 Hz 100 Hz 125 Hz 150 Hz

Lakshan Dumpa by Lakshan Dumpa , 24, India

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4 solutions

Samarpit Swain
Feb 22, 2014

f={(340+60)/(340-20)}.100= 125Hz

2 Helpful 0 Interesting 0 Brilliant 0 Confused
Karen Adelan
Mar 9, 2014

fL=fS[v + vL/ v - vS] fL = 100Hz [340m/s + 60m/2 / 340m/s - 20m/s] fL = 125Hz

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Use Doppler Effect.

Fo=Fs[(Va+Vo)/(Va-Vs)]

Where:

Fo=the frequency heard by the Observer (Calvin)

Vo=the Velocity of the observer

Fs=Frequency produced by the source (Car Horn)

Vs=Velocity of the source

Va= Velocity of wave (sound) in said medium (air)

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Shamik Banerjee
Feb 24, 2014

Doppler Effect

0 Helpful 0 Interesting 0 Brilliant 0 Confused

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