A police dog named Hooch is taking a police driving test. Hooch drives a police
ID: 1560141 • Letter: A
Question
A police dog named Hooch is taking a police driving test. Hooch drives a police car traveling at 70 m/s with a siren that emits a steady frequency of 850Hz. A duck named Ben (Affleck) pretends to be a bad guy whom Hooch must apprehend. Ben drives a delivery truck. a) In the first test Ben's truck is not moving, and Hooch is driving towards Ben. What frequency does Ben hear in the stationary delivery truck? What frequency does Hooch hear reflected back to him? b) In the second test, Hooch is chasing Ben. Ben's truck is moving at 50 m/s away from Hooch (but Hooch is catching up.) What frequency does Ben hear in the delivery truck? What frequency does Hooch hear reflected back to him in the police car? c) Hooch drives past Ben. Ben is still traveling at 50 m/s, but now Hooch is in front of him traveling away. What frequency does Ben hear in the delivery truck? What frequency does Hooch hear reflected back to him?Explanation / Answer
(a)
frequency heard by Ben f1 = (v*f0)/(v-v1)
f0 = 850 Hz
v = speed of sound = 343 m/s
v1 = speed of Hooch
f1 = (343*850)/(343-70)
f1 = 1068 Hz
after reflection
frequency heard by Hooch f2 = (v+v1)*f1/v
f2 = 1068*(343+70)/343
f2 = 1286 Hz
===================
(b)
frequency heard by Ben f1 = ((v-v0)*f0)/(v-v1)
f0 = 850 Hz
v = speed of sound = 343 m/s
v0 = 50 m/s
v1 = speed of Hooch
f1 = (343-50)*850)/(343-70)
f1 = 912.3 Hz
after reflection
frequency heard by Hooch f2 = (v+v1)*f1/(v+v0)
f2 = 912.3*(343+70)/(343+50)
f2 = 958.72 Hz
===================
(c)
frequency heard by Ben f1 = ((v+v0)*f0)/(v+v1)
f0 = 850 Hz
v = speed of sound = 343 m/s
v0 = 50 m/s
v1 = speed of Hooch
f1 = (343+50)*850)/(343+70)
f1 = 808.84 Hz
after reflection
frequency heard by Hooch f2 = (v-v1)*f1/(v-v0)
f2 = 808.84*(343-70)/(343-50)
f2 = 753.63 Hz
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