You are driving along a highway at 25.5 m/s when you hear a siren. You look in t

Question

You are driving along a highway at 25.5 m/s when you hear a siren. You look in the rear-view mirror and see a police car approaching you from behind with a constant speed. The frequency of the siren that you hear is 1220. Hz. Right after the police car passes you, the frequency of the siren that you hear is 1170. Hz.

a) How fast was the police car moving?

b) You are so nervous after the police car passes you that you pull off the road and stop. Then you hear another siren, this time from an ambulance approaching from behind. The frequency of its siren that you hear is 1240. Hz. Once it passes, the frequency is 1030. Hz. What is the actual frequency of the ambulances siren?

Explanation / Answer

a) 1220 = (334-25.5)/(334-v)*f1

and 1170 = (334+25.5)/(334+v)*f1

solving these quations we get v = 32.43 m/s

b)1240 = 334/(334-v)

and 1030 = 334/(334+v)

solving we get v = 30.89 m/s

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