NEET Questions Solved


An observer standing at station observes frequency 219 Hz when a train approaches and 184 Hz when train goes away from him. If velocity of sound in air is 340 m/s, then velocity of train and actual frequency of whistle will be 

(1) 15.5ms1,200Hz

(2) 19.5ms1,205Hz

(3) 29.5ms1,200Hz

(4) 32.5ms1,205Hz

(3) When train is approaching frequency heard by the observer is

na=nvvvS219=n340340vS …(i)

when train is receding (goes away), frequency heard by the observer is

nr=nvv+vs184=n340340+vs …(ii)

On solving equation (i) and (ii) we get

n=200Hz and vS=29.5m/s.

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