I keep getting this wrong! Help! An ambulance is traveling East at 20m/s. The si
ID: 1596688 • Letter: I
Question
I keep getting this wrong! Help!
An ambulance is traveling East at 20m/s. The siren emits a fixed frequency of 210Hz. Each of the following cars is traveling down the road as described. Rank the cars according to the frequency the driver will hear. Select 1 for the car which will hear the highest frequency. Remember that if the frequency is the same, select the same rank and skip the next number. I really suggest drawing a picture to help sort this out. Keep in mind the relative speed - How fast does it seem the ambulance is moving towards or away from each driver? A car driving East at a speed of 15m/s. The car is behind the ambulance. A car driving East at a speed of 20m/s. The car is behind the ambulance. A car driving West at a speed of 25m/s. The car is moving towards the ambulance. A car sitting stationary at the side of the road watching the oncoming ambulance.Explanation / Answer
1.)
Va = speed of ambulance or source = 20 m/s
Vc = speed of car or listener = 15 m/s
V = speed of sound = 343
f = actual frequency = 210
f' = frequency heard
using the formula
f' = (V - Vc) f/(V + Va) = (343 - 0) (210)/(343 + 5) = 207 Hz
rank 4
b)
Va = speed of ambulance or source = 20 m/s
Vc = speed of car or listener = 20 m/s
V = speed of sound = 343
f = actual frequency = 210
f' = frequency heard
using the formula
f' = (V - Vc) f/(V - Va) = (343 - 20) (210)/(343 - 20) = 210 Hz
rank 3
c)
Va = speed of ambulance or source = 20 m/s
Vc = speed of car or listener = 25 m/s west
V = speed of sound = 343
f = actual frequency = 210
f' = frequency heard
using the formula
f' = (V - Vc) f/(V + Va) = (343 - 25) (210)/(343 + 20) = 213.25 Hz
Rank 2
d)
Va = speed of ambulance or source = 20 m/s
Vc = speed of car or listener = 0
V = speed of sound = 343
f = actual frequency = 210
f' = frequency heard
using the formula
f' = (V - Vc) f/(V - Va) = (343 - 0) (210)/(343 - 20) = 223 Hz
Rank 1