A car travels straight toward a stationary observer at 20 m/s
PHYSICS · Single correct · AP · Physics 2: Algebra-based · Waves Sound and Physical Optics · Waves Sound and Physical Optics
Problem
A car travels straight toward a stationary observer at 20 m/s. A whistle attached to the rim of one of the car’s wheels emits a steady 500 Hz tone. The wheel has a radius of 0.318 m and rotates at 10 revolutions per second in the forward direction. Neglecting any effects other than the rim’s motion, at which point on the rim will the observer momentarily hear the whistle at its rest frequency?
(a) No point on the rim can ever produce the rest frequency under the given conditions.
(b) The bottom of the wheel, where the rim moves backward relative to the car.
(c) The top of the wheel, where the rim moves forward relative to the car.
(d) The point on the rim closest to the observer’s right-hand side, where the rim’s motion is lateral.