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
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When train is approaching frequency heard by the observer is
$n_a = n \left(\frac{V}{V - v_s}\right)$ $\Rightarrow 219 = n \left(\frac{340}{340 - v_s}\right) \quad \ldots (i)$ when train is receding (goes away), frequency heard by the observer is $n_r = n \left(\frac{V}{V + v_s}\right)$ $\Rightarrow 184 = n \left(\frac{340}{340 + v_s}\right) \quad \ldots (ii)$ On solving equation (i) and (ii) we get n = 200Hz and $v_s = 29.5m/s$.
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