You hear a high pitch as he comes toward you, lower as he leaves
So the actual frequency is lower than you hear.
In fact you know it is between 195 and 147
Fl = [(v + vl)/(v+vs) ] Fs
where
Fl = frequency heard
Fs = Frequency of source
v = v sound
vl = v listener
vs = v source
direction from listener TOWARD source is Positive
HERE:
You say v = 343.52
vl = police officer = 0
so
Fl = [v/(v+vs)]Fs
at first vs is negative, opposite from listener toward source
195 = [343.52/ (343.52 - vs)] Fs
147 = [343.52/(343.52 + vs)] Fs
eliminate Fs and solve for vs
A police officer with good ears hears an approaching motorcycle. The engine sound he eats as the bike approached is 195 Hz.
a) Is the actual sound the bike makes higher or lower in pitch?
b) After the bike passes he hears 147 Hz as the perceived pitch. If it was a nice 20 degree Celsius day, how fast was the bike moving.
-------
for a) I think that the actual sound in higher in pitch.
for b) I found the speed in air and got 343.52 m/s as my answer. I am not sure how to continue the question from there.
1 answer
1 answer