How Does the Doppler Effect Explain the Ambulance Siren Frequency Change?

[zipking1988]

some exam question(help help !)

Q1.A train traveling at 30 km/h is approached from behind by an ambulance sounding its siren.The ambulance ,which is traveling at a constant speed along a road parallel to the railroad,passes the train and subsequently stops at a distant point ahead of the train .The change in the frequency of the siren'sound was measure on the train .It was observed that frequency f' just after the ambulance stopped was the same as the frequency when the ambulance approached from far behind the train

Q2 What is the relationships between the magnitudes of f' and f ,the frequency of the siren 's sound source ?also ,what was the approximate speed at the ambulance traveled?from 1-6 below choose the correct combination

http://img3.imageshack.us/img3/3053/capture1gb.jpg

 

[zipking1988]

Q2:As show in the figure below ,circuit A is formed by connecting two direct power sources(electromotive force :15v and 5 v ) and two capacitor (capacitor 1uF and C),and circuit B is formed by connecting the same two power sources and two resistors (resistance:1kohm and R) .The connection point between the two power sources is grounded ,and the electric potential at that point is zero.The internal resistance of the power sources is negligible

http://img3.imageshack.us/img3/1958/capture2an.jpg

Q4 The electirc potential needs to be kept at zero at point a (connection between the two capacitor)in circuit A and at point b(connection between the two resistors) in circuit B.What values of C and R necessary to satisfy this condition ?from 1-6 below choose the best condition .
http://img11.imageshack.us/img11/3249/capture3r.jpg

 

[zipking1988]

A charge Q is placed at the origin (0,0) of an x-y plane.The proportionality constant of Coulomb 's law is donated as Ko .

Q1 ,From 1-5 below choose the answer that correctly represents field E at point (x.y) ,where E=(Ex,Ey).here Ex is the x-component of E and Ey is the y-component of E .
http://img11.imageshack.us/img11/9504/capture444.jpg

 

[zipking1988]

Any please i need your help !

 

[ApexOfDE]

It seems that you don't know rules in PF. Please take a look on this thread if you still want to find assistance in PF. https://www.physicsforums.com/showthread.php?t=94379"