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Assignment
 An ambulance travels down a high way at a speed of 75.0 mi/h, its siren emitting sound at a frequency of 400 Hz. What frequency is heard by a passenger in a car travelling at 55.0 mi/h in the opposite direction as the car (a) approaches? (b) Moves away from the ambulance?
 A train moving at a speed of 40.0 m/s sounds its whistle, which has a frequency of 500 Hz. Determine the frequency heard by a stationary observer as the train approaches the observer also find the frequency heard by the stationary observer as the train recedes from the observer.

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