In this lesson, we will learn how to calculate the change in the frequency of waves that are emitted by a source that is moving relative to the observer.

Q1:

A hawk swoops down to catch a mouse, screeching as it does so. The hawk approaches the mouse at a speed of 25.0 m/s, and the frequency of the screech is 3 5 0 0 Hz. What is the frequency of the screech as heard by the mouse? Use a value of 331 m/s for the speed of sound in air.

Q2:

A commuter train approaches a crossing and blows its horn to make a note of frequency 200 Hz. An observer at the crossing measures the frequency of the train’s horn as 208 Hz. The speed of sound in the train’s vicinity is 335 m/s.

What is the speed of the train?

If the train’s speed remains constant, what frequency does the observer measure as the train recedes from them?

Q3:

An ambulance with a siren blaring is approaching an accident scene. The ambulance is moving at 70.00 mph. A nurse is approaching the scene from the opposite direction, running at . What frequency does the nurse observe? Assume the speed of sound is .

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