A police car siren emits a 900 Hz tone as the car travels due east at 30 m/s

PHYSICS · Single correct · A Level · Physics · Waves · Waves

Problem

A police car siren emits a 900 Hz tone as the car travels due east at 30 m/s. A motorist in another car is moving due west (directly toward the police car) at 20 m/s on the same straight road. The speed of sound in air is 343 m/s. What frequency does the motorist hear? (a) 9.86×102 Hz9.86\times10^{2}\text{ Hz} (b) 9.30×102 Hz9.30\times10^{2}\text{ Hz} (c) 1.04×103 Hz1.04\times10^{3}\text{ Hz} (d) 8.80×102 Hz8.80\times10^{2}\text{ Hz}

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