wave_mechanics mock_test_waves_and_acoustics Question 6
A source of sound of frequency$ f {1} $ is placed on the ground. A detector placed at a height is released from rest towards this source. The observed frequency$ f{obs}(Hz) $ is plotted against time $ t $ (sec). The speed of sound in air is 300 m/s. Find$ f _{1} $
$ (g=10m/s^{2}) $
Options:
A) $ 0.5\times 10^{3}Hz $
B) $ 1\times 10^{3}Hz $
C) $ 0.25\times 10^{3} $
D) $ 0.25\times 10^{3}Hz $
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Answer:
Correct Answer: B
Solution:
[b] $ f=( \frac{v+v _{0}}{v} )f _{1}=f _{1}+f _{1}\frac{v _{0}}{v} $
$ v _{0}=gt $ So $ f=f _{1}+( \frac{f _{1}g}{v} )t $ Slope of graph $ =\frac{f _{1}g}{v}\frac{2\times 10^{3}-f _{1}}{30}=\frac{(f _{1})(10)}{300} $ Or $ f _{1}=10^{3} $ Hz
BETA
