Practice Doppler Effect in Physics

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

Worksheet PDF Free Answer-key PDF Family

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.

Showing a random 20 of 50 problems.

Example 1

easy

Light from a star is shifted to higher frequency (blueshift). Approaching or receding?

Example 2

easy

A motorcycle revs while parked. You walk toward it at constant speed. Do you hear the engine higher or lower?

Example 3

medium

A stationary observer hears

f' = 550

Hz from a source emitting

f = 500

Hz;

v = 340

m/s. Is the source approaching or receding, and at what speed?

Example 4

easy

Does the Doppler effect change the frequency actually emitted by the source?

Example 5

challenge

Two cars travel directly toward each other on a road; each at

v = 25

m/s. Car A's horn emits

f = 450

Hz;

v_{snd} = 340

m/s. What frequency does car B hear?

Example 6

medium

A whistle emits at

400

Hz; a runner moves away at

5

m/s;

v = 340

m/s. Find observed frequency.

Example 7

medium

A source (

f = 800

Hz) recedes at

v_s = 40

m/s from a stationary observer;

v = 340

m/s. Find

f'

Example 8

medium

A car horn

f = 500

Hz; the observer cycles toward the parked car at

v_o = 5

m/s;

v = 340

m/s. Find observed frequency.

Example 9

medium

A stationary source emits

f = 600

Hz; observer drives away at

v_o = 30

m/s;

v = 340

m/s. Find

f'

Example 10

hard

A bat emits

40

kHz toward an insect moving away at

5

m/s;

v = 340

m/s. Find the frequency the insect 'hears' using

f' = f(v - v_o)/v

Example 11

easy

Light from a distant galaxy is shifted to lower frequency (redshift). Is the galaxy approaching or receding?

Example 12

hard

Police 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.

Example 13

easy

A police siren whose pitch you hear keeps dropping. Is the car approaching or moving away?

Example 14

medium

A train whistle (

f = 600

Hz) now recedes at

v_s = 20

m/s;

v = 340

m/s. Use

f' = f\,v/(v + v_s)

Example 15

medium

A 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 16

medium

An observer moves away from a stationary source (

f = 400

Hz) at

v_o = 34

m/s;

v = 340

m/s. Use

f' = f\,(v - v_o)/v

Example 17

challenge

A sound source approaches a wall at

v_s = 34

m/s emitting

f = 500

Hz (

v = 340

m/s). The wall reflects the sound back to the moving source. The wall first receives

f_1 = f\,v/(v - v_s)

; it then re-emits

f_1

and the approaching source (now observer) hears

f_2 = f_1(v + v_s)/v

. Find

f_2

Example 18

medium

Same source (

f = 500

Hz,

v_s = 34

m/s) now moves away;

v = 340

m/s. Use

f' = f\,v/(v + v_s)

Example 19

medium

Why can't you use the simple sound Doppler formula for light from a fast-moving star?

Example 20

easy

An ambulance siren moves away from you. Does the observed pitch rise or fall?

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Related Concepts

Frequency Wave Speed Redshift