Answer:
A)828.8Hz
B)869.2Hz
Explanation:
Here is a complete question;
What frequency is received by a person watching an oncoming ambulance moving at 115 km/h and emitting a steady 753 Hz sound from its siren? Speed of sound is 345m/s
b. What frequency does she receive after the ambulance has passed?
Vs= speed of the ambulance
, We convert to m/s for unit consistency
= 115 km/h= 115km× 1000m/1m × 1hr/3600s= 31.94m/s
Dopler effect is when observed frequency of wave changes with respect to the source or when observed moves relative to transmitting medium can be expressed as
f'=[ (v + vo)/(v- vs)]*f
=[ (v )/(v- vs)]*f
The sign vo and vs depends on vthe direction of the velocity
f= frequency of ambulance siren= 753Hz
v= speed of sound in air= 345m/s
Vo= speed of observer= 0
A) we are to determine the f' of ambulance as heard by person as ambulance approaching.
To find the frequency f' observed by the person we use the expresion below
Then substitute the values
f'=[ (v )/(v- vs)]*f
=[ (345)/(345-31.94)]×753
= 828.8Hz
B)What frequency does she receive after the ambulance has passed?
To find the frequency f' observed by the person we use the expresion below
Then substitute the values
f'=[ (v )/(v + vs)]*f
=[ (345)/(345 + 31.94)]×753
= 869.2Hz
=
