# calculate frequincy off sound

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An Ambulance  approaches a stationary pedestrian at a constant velocity of 45m.s-1 .The siren of the ambulance howls at a constant frequency. the pedestrian uses a tracking device and measures the frequency that she can hear as 909Hz at first, and then as 704Hz. The speed of sound in air is constant.

6.1. Calculate the frequency of the sound produced by the siren.

6.2. How will the value of the frequency measured by the pedestrian change while the ambulance approaches her if the following changes take place?

6.3.1. the constant speed of the ambulance is 50m.s-1.

6.3.2. the frequency at which the siren howls increases

6.3.3 the speed of the sound in air is less