## Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (3rd Edition)

(a) We can convert the speed to units of m/s $v = (90~km/h)(\frac{1000~m}{1~km})(\frac{1~hr}{3600~s})$ $v = 25~m/s$ We can find the frequency heard by a stationary observer in front of the car. $f' = \frac{f}{(1-\frac{v_{source}}{v_{snd}})}$ $f' = \frac{600~Hz}{(1-\frac{25~m/s}{343~m/s}~)}$ $f' = 647~Hz$ The frequency heard is 647 Hz (b) We can find the frequency heard by a stationary observer behind the car. $f' = \frac{f}{(1+\frac{v_{source}}{v_{snd}})}$ $f' = \frac{600~Hz}{(1+\frac{25~m/s}{343~m/s}~)}$ $f' = 559~Hz$ The frequency heard is 559 Hz