A) 50 Hz
B) 85 Hz
C) 100 Hz
D) 150 Hz
Correct Answer: C
Solution :
By Dopplers Effect When observer is moving with velocity \[{{v}_{0}},\]towards a source at rest then approach frequency \[{{N}_{Approach}}=N\left( \frac{v+{{v}_{0}}}{v} \right)\] where \[N=850\,Hz,\,v=340\,m{{s}^{-1}},\,{{v}_{0}}=72\,km\,{{h}^{-1}}\] \[=20\,m{{s}^{-1}}=850\,\left( \frac{340+20}{340} \right)\] Similarly, when observer is moving away from source, then \[{{N}_{Separation}}=N\left( \frac{v-{{v}_{0}}}{v} \right)=850\left( \frac{340-20}{340} \right)\] The different of the two frequency, \[{{N}_{Approach}}-{{N}_{Separation}}\] \[=850\left( \frac{360}{340} \right)-850\left( \frac{320}{340} \right)\] \[=\frac{850}{340}\times 40=\frac{850}{8.5}=100\,Hz\]You need to login to perform this action.
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