A bicycle messenger rides along a straight, quiet street toward a stationary security vehicle whose siren is sounding steadily at 700 Hz. The messenger pedals at 10 m/s relative to the still air, then continues past the vehicle at the same speed but in the opposite direction. Take the speed of sound in air to be 343 m/s.
(a) Determine the frequency the messenger hears while approaching the security vehicle.
(b) Determine the frequency the messenger hears after passing and moving directly away from the vehicle.
(c) While still approaching, the messenger momentarily stops pedaling and coasts to a speed of 5 m/s before resuming 10 m/s. Calculate the percent change in the observed frequency that results from this temporary speed reduction.