1) Hearing the siren of an approaching fire truck, you pull over to the side of
ID: 1389769 • Letter: 1
Question
1) Hearing the siren of an approaching fire truck, you pull over to the side of the road and stop. As the truck approaches, you hear a tone of 460
Hz ; as the truck recedes, you hear a tone of 400Hz .
How much time will it take for the truck to get from your position to the fire 4.0
A train on one track moves in the same direction as a second train on the adjacent track. The first train, which is ahead of the second train and moves with a speed of 35.6
m/s , blows a horn whose frequency is 124Hz .
If the frequency heard on the second train is 135
Hz , what is its speed?
Explanation / Answer
f*= f ( 1+ velocity obj./ Vel. sound)
460= 400 (1+ Vel. Ft/ 343)
Velocity of firetruck= 51.45 m/s
Now find time:
x-xo= ViT + (1/2)(A)(t^2)
4000 meters = (51.45 m/s)(t)
Time = 77.7SEC
f'/f = (vsound + vobserver)/(vsound + vsource)
Put the values and calculate vobserver.
I am assuming vsound = 340 m/s. Use the value given in your book
135/124 = (340 + vobserver)/(340 + 35.6)
vobserver = 68.91 m/s
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