Practice Doppler Effect in Physics
Use these practice problems to test your method after reviewing the concept explanation and worked examples.
Quick Recap
The change in the observed frequency (and wavelength) of a wave when the source and the observer are in relative motion.
An ambulance siren sounds higher-pitched approaching, lower-pitched receding.
Example 1
easyAn ambulance siren emits sound at 700 \text{ Hz}. As the ambulance approaches you at 30 \text{ m/s}, what frequency do you hear? Use v_{\text{sound}} = 340 \text{ m/s}.
Example 2
mediumA train whistle blows at 500 \text{ Hz}. You are stationary and hear 475 \text{ Hz}. Is the train approaching or moving away? What is the train's speed? Use v_{\text{sound}} = 340 \text{ m/s}.
Example 3
mediumA car horn emits 400 \text{ Hz}. You drive toward the stationary car at 20 \text{ m/s}. What frequency do you hear? Use v_{\text{sound}} = 340 \text{ m/s}.
Example 4
hardPolice radar emits microwaves at 10.5 \text{ GHz}. The reflected signal from an approaching car has a frequency shift of 3500 \text{ Hz}. What is the car's speed? Use c = 3 \times 10^8 \text{ m/s} and the Doppler formula \Delta f = \frac{2v_s f}{c} for electromagnetic waves.