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ravi pratap Grade: 12
        

An engine whestles at a frequency of 256Hz moves towards  a wall with a velocity of 50m/s. How many number of beats will be sounded to the engine?

8 years ago

Answers : (1)

devashish trivedi
8 Points
										

Doppler's fomula is


           n' = n (v -vo)/(v-vs)


where n' = apprant frequency


           n = original frequency


         v = spped of sound in air that is 330 m/s


      vo = speed of observer


     vs = speed of the source


Here n = 256 hz vo = 0 vs = 50m/s pluging in the values we will get n = 497 hz


now with this frequency the sond will reflect from the wall so the source will be stationary


we will again use the same formula


                                                       n" = n (v -vo)/(v-vs)


now vo = 50m/s , vs = 0 and v =330m/s n" = frequency heard by the observer


now pluging in the values we will have


                                                    n" = 497(330 - 50)/(330 - 0)


                                                           = 497x 280/330


                                                          = 422hz so the no of beats heard by the observer is n" - n = 422 - 256=      166 beats per second

8 years ago
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