Consider an ambulance traveling north toward an accident scene at 29.6 m/s and e
ID: 1574884 • Letter: C
Question
Consider an ambulance traveling north toward an accident scene at 29.6 m/s and emitting a frequency heard within the ambulance as 1420 Hz. A variety of observers hear the ambulance. Determine the frequency that each hears. a) An accident victim lying motionless in the street ahead of the ambulance. b) A helpful witness running south toward the ambulance at 5.4 m/s. c) The motorist who struck the victim, fleeing the scene to the north at 34.8 m/s. d) An ambulance chaser following the ambulance at 29.6 m/s. e) Another motorist south of the ambulance and traveling south at 16.2 m/s.
Explanation / Answer
Using Doppler's effect in each cases:
A.
when Source is moving towards stationary observaer
f1 = f0*V/(V - Vs)
V = speed of sound = 343 m/sec
Vs = speed of source
f1 = 1420*343/(343 - 29.6)
f1 = 1554.12 Hz
B.
when source and observer are moving towards each other
f1 = f0*(V + Vo)/(V - Vs)
f1 = 1420*(343 + 5.4)/(343 - 29.6)
f1 = 1578.58 Hz
C.
When the Source is approaching the Stationary observer and observer moving away from it
f1 = f0*(V - Vo)/(V - Vs)
f1 = 1420*(343 - 34.8)/(343 - 29.6)
f1 = 1396.44 Hz
D.
When the Observer is approaching the Stationary source and source moving away from it
f1 = f0*(V + Vo)/(V + Vs)
f1 = 1420*(343 + 29.6)/(343 + 29.6)
f1 = 1420 Hz
E.
When Source and object are moving away from each other
f1 = f0*(V - Vo)/(V + Vs)
f1 = 1420*(343 - 16.2)/(343 + 29.6)
f1 = 1245.45 Hz