Question

A motorcyclist is traveling north on a road at a speed of 29.0 m/s. A fire truck, traveling south at a speed of 49.0 m/s, approaches with its siren producing sound at a frequency of 2550 Hz. (Enter your answers in Hz. Assume that the speed of sound in air is 343 m/s.)

(a)

What frequency does the motorcyclist observe as the fire truck approaches? (Enter your answer to the nearest integer.)

(b)

What frequency does the motorcyclist detect after the fire truck passes her?

Hz

(c)

Repeat parts (a) and (b) for the case when the fire truck is traveling northbound.

while fire truck overtakes __________Hz

after fire truck passes __________Hz

Answer 1

here , we need to use doppler effect

logic - whenever a sound source approach , a listener will hear a higher frequency and when it recedes, listener will hear lower frequency

_________________

(a)

f = f_o ( v +/- v_observer / v + / - v_source )

f = 2550 ( 343 + 29 / 343 - 49)

f = 3226.5 Hz

_______________

(b)

f = 2550 ( 343 - 29 / 343 + 49)

f = 2042.6 Hz

_________________

(c)

when truck overtakes

f = 2550 ( 343 - 29 / 343 - 49)

f = 2723.5 Hz

_________________

(d)

f = 2550 ( 343 + 29 / 343 +  49)

f = 2419.9 hz