## College Physics (4th Edition)

Published by McGraw-Hill Education

# Chapter 12 - Problems - Page 464: 45

#### Answer

(a) The frequency of the sound received by a stationary observer is $2.0~kHz$ (b) The frequency of the sound received by a stationary observer is $666.7~Hz$

#### Work Step by Step

(a) We can find the speed of the source: $v_s = (0.50)~(343~m/s) = 171.5~m/s$ We can use the equation for the Doppler effect when the source is approaching: $f_o = \left(\frac{v}{v-v_s}\right)~f_s$ $f_o = \left(\frac{343~m/s}{343~m/s-171.5~m/s}\right)~(1.0~kHz)$ $f_o = 2.0~kHz$ The frequency of the sound received by a stationary observer is $2.0~kHz$ (b) We can use the equation for the Doppler effect when the source is moving away: $f_o = \left(\frac{v}{v+v_s}\right)~f_s$ $f_o = \left(\frac{343~m/s}{343~m/s+171.5~m/s}\right)~(1000~Hz)$ $f_o = 666.7~Hz$ The frequency of the sound received by a stationary observer is $666.7~Hz$

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