A) 300cycle/sec
B) 320 cycle/sec
C) 340 cycle/sec
D) 330 cycle/sec
Correct Answer: A
Solution :
As sound and observer are approaching each other hence, by Doppler effect appearent frequency will be. \[f={{f}_{0}}\left[ \frac{V+{{V}_{0}}}{V-{{V}_{S}}} \right]\] ?..(i) Where, V is the velocity of sound in air or vaccum Here, \[f=400C/S,\] \[{{V}_{0}}={{V}_{s}}=50m/s\] Putting value in equation (i) we get. \[400={{f}_{0}}\left[ \frac{340+50}{340-50} \right]\] \[(\because \,V=340m/s)\] \[\Rightarrow \] \[{{f}_{0}}=\frac{400\times 290}{390}\] \[\Rightarrow \] \[{{f}_{0}}=297.44\] \[{{f}_{0}}=330\] cyles/sec.
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