5. If the four-wheeler has a top speed of 25 mph, will Stanley and his friend be able to use this method to determine if the whistle is functioning?

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Answer 1 · 2018-05-01T15:50:27

yes

the four wheeler has top speed of 25 miles per hour.

and both are sitting in it .

one sounds a whistle and the source is moving with a good speed

the other ,the observer is sitting with him and moving with same

speed so for him relative velocity of sound will be same as the

velocity of sound in situation when both were stationary.

when both the observer and the source of sound are moving with

same velocity. - the velocity of one with respect to other will be zero.

so one will observe the same frequency as the other is producing.

however if Stanely drops his friend at the sidewalk and whistles

away with speed of 25 mph then the friend can hear the sound

with altered frequency and that's due to the doppler shift

#25 mph = 25 /(60 .60) mipsec# =( 25 x 1.6 x 10^3 m)/3600 sec

=8,5 m/sec.

so the friend will hear a frequency # f'#

#f' = {v / (v +vs)} .f #

where #v= #velocity of sound and # vs # is velocity of source (the vehicle)
so he will hear an altered frequency and can not test.