Problem 12.62 Part A A police car sounding a siren with a trequency of 1570 Hz i
ID: 1781752 • Letter: P
Question
Problem 12.62 Part A A police car sounding a siren with a trequency of 1570 Hz is traveling at 130 km/h What frequencies does an observer standing next to the road hear as the car approaches and as it recedes? Express your answers using three significant figures separated by a comma. Hz Submit My Answers Sive We Part B What frequencies are heard in a car traveling at 90.0 km/h in the opposite direction before and after passing the police car? Express your answers using three significant figures separated by a comma. Hz My Answers Give Up Part C The polioe car passes a car traveling in the same direction at 80.0 km/h. What two trequencies are heard in this car? Express your answers using three significant figures separated by a comma Hz Submit My Answers Give.Explanation / Answer
Given,
fo = 1570 Hz and V = 130 km/hr = 36.11 m/s
We know that the observed frequency and the emitted frequency are related as:
f = (V + Vr)/(V + Vs) x fo
where, V is the velocity of sound, Vr is the that of reciever and Vs is that of source ;
1)since the observer is standing, Vr = 0
f(approac) = ( 343 / (343 - 36.11) ) x 1570 = 1754.73 Hz
f(receds) = (343/ 343 + 36.11 ) ) x 1570= 1420.45Hz
b) Now Vr = 90 km/h = 25 m/s
f(approac) = ( 343 + 25 / (343 - 36.11) ) x 1570 = 1882.6 Hz
f(receds) = (343 - 25 / 343 + 36.11) ) ) x 1570= 1316.9 Hz
c) Vr = 80 km/h = 22.22 m/s
f(approac) = ( 343 -22.22 / (343 - 36.11)) ) x 1570 = 1641.05 Hz
f(receds) = (343 + 22.22/ 343 + 36.11) ) )x 1570 = 1512.47 Hz