A) \[40\text{ }m{{s}^{-1}}\]
B) \[20\text{ }m{{s}^{-1}}\]
C) \[340\text{ }m{{s}^{-1}}\]
D) \[\text{180 }m{{s}^{-1}}\]
E) \[50\text{ }m{{s}^{-1}}\]
Correct Answer: A
Solution :
From Dopplers effect, perceived frequency \[f=f\left( \frac{v-{{v}_{o}}}{v-{{v}_{s}}} \right)\] \[\frac{9}{8}=\frac{340}{340-{{v}_{s}}}\] \[\Rightarrow \] \[9(340-{{v}_{s}})=8\times 340\] \[\Rightarrow \] \[{{v}_{s}}=37.7\,m{{s}^{-1}}\approx 40\,m{{s}^{-1}}\]
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