Doppler Tutorial 3

1. A vampire bat flies at 12 m.s-1 directly toward a cave wall and emits an ultrasound of 45kHz. Assume that the speed of the sound is 340 m.s-1.

1.1 What is meant by the term "ultrasound"?
1.1 frequency above that which a human can hear.
1.2 Calculate the frequency that would be picked up at the wall, if a receiver was placed at the wall.
1.2 Here is the drawing. The wall would be the "listener".

Substituting into the equation
1.3 The sound would reflect off the wall, and be heard by the bat. At what frequency would the bat hear it's own reflected sound?
The wall must now be considered the source with a frequency of 46 646,34Hz.
The bat becomes the listener.
The bat is STILL approaching the wall, and is opposite to the sound direction.
Remember that the sound line v is always positive, so the bat becomes negative.

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V. Gokal