ku1005
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Hey guys...or ladies...um...just wondering what I have done wrong for the following Q, it is an online Q i am doing and it tells me my answer is incorrect?
Q) "A car alarm is emitting sound waves of frequency 520 Hz. You are on a motorcycle, traveling directly away from the car."
"How fast must you be traveling if you detect a frequency of 490 Hz?
Enter your speed as a positive number. Take the speed of sound to be 344 m/s.
It seems fairly striaght forward, so I used the doppler effect (ie the wavelength must be greater and hence the frequency less if moving away)
so...
f(effetive) = v/(v+vl) . f
where vl = velocity of listener...
so i have
344/(344 . vl) . 520 = 490
solving for vl gives...21.06 ms^-1 roughly
so therfore, bke must be moving at 21.06ms^-1 ?
BUT it tells me this answer is incorrect??
any ideas appreciated!
cheers
rhys
Q) "A car alarm is emitting sound waves of frequency 520 Hz. You are on a motorcycle, traveling directly away from the car."
"How fast must you be traveling if you detect a frequency of 490 Hz?
Enter your speed as a positive number. Take the speed of sound to be 344 m/s.
It seems fairly striaght forward, so I used the doppler effect (ie the wavelength must be greater and hence the frequency less if moving away)
so...
f(effetive) = v/(v+vl) . f
where vl = velocity of listener...
so i have
344/(344 . vl) . 520 = 490
solving for vl gives...21.06 ms^-1 roughly
so therfore, bke must be moving at 21.06ms^-1 ?
BUT it tells me this answer is incorrect??
any ideas appreciated!
cheers
rhys