A train blowing a whistle of frequency 320 Hz approaches an observer standing on the platform at a speed of 66 m s - 1 . The frequency observed by the observer will be (given speed of sound = 330 m s - 1 ) ______ Hz .

Step-by-step solution

Using Doppler's effect, the frequency observed by the observer when the train moves towards the stationary observer is f app = f v v - v s Given here, v s = 330   m   s - 1   and   v = 66   m   s - 1 Putting the values, f app = 320 330 330 - 66 ⇒ f app = 400   Hz .