A) 268 Hz
B) 271 Hz
C) 368 Hz
D) 250 Hz
Correct Answer: B
Solution :
Speed of source \[{{\upsilon }_{s}}=20\,m/s\] Frequency\[v=240\,Hz\] Speed of observer \[{{\upsilon }_{0}}=20\,\,m/s\] Speed of sound in in air\[~=330\text{ }m/s\] (given) From the Doppler's effect the apparent frequency heard by the observer, when he is moving towards the source is given by: \[v'=\left( \frac{\upsilon +{{\upsilon }_{0}}}{\upsilon -{{\upsilon }_{s}}} \right)\times v\] \[=\left( \frac{330+20}{330-20} \right)\times 246=27.96\] \[=271\,Hz\]You need to login to perform this action.
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