Unless indicated otherwise, assume the speed of sound in air to be v = 344 m/s. A car alarm is emitting sound waves of frequency 520 Hz. You are on a motorcycle, traveling directly away from the parked car. How fast must you be traveling if you detect a frequency of 490 Hz?
Solution 49E Let your speed be x. Given that the speed of sound v = 344 m/s The frequency of the car alarm = 520 Hz The frequency heard by you = 490 Hz vx Therefore, 490 Hz = v × 520 Hz 490 vx 520 = v 490 = 1 x 520 v x = v(1 490) 520 490 x = 344 × (1 520 ) m/s x = 19.8 m/s Your travel speed is approximately 19.8 m/ s.