The Doppler effect

Answer Key - Grade 11 Science Worksheet

Circle the best answer, or write your answer on the line.

1. 1.

   A 1000 Hz toy buzzer on a cart approaches at 5 m/s. With sound at 343.3 m/s in 20 °C air, what frequency does a listener ahead hear, to the nearest tenth, Bo?

   1014.8 Hz
2. 2.

   A 300 Hz train horn approaches at 30 m/s. With sound at 343.3 m/s in 20 °C air, what frequency does a listener ahead hear, to the nearest tenth, Esme?

   328.7 Hz

3. Read this first

   A 400 Hz train horn passing at different speeds, in 20 °C air (worked out with 343.3 m/s for sound)

   Train speed (m/s)	Heard approaching (Hz)	Heard moving away (Hz)
   10	412	388.7
   20	424.7	378
   30	438.3	367.9

4. 3.

   Using the table, how does the train's speed change the shift, Jun?

   • Faster trains make smaller shifts
   • Faster trains make bigger shifts
   • Speed makes no difference
5. 4.

   Using the table, what does a listener hear as a 20 m/s train moves away, Kira?

   • 378.0 Hz
   • 400 Hz
   • 424.7 Hz
6. 5.

   Using the table, by about how many hertz does the pitch drop as a 10 m/s train passes, Luz?

   • About 23 Hz
   • About 400 Hz
   • About 12 Hz
7. 6.

   Light from a distant galaxy is shifted toward longer, redder wavelengths. What does that show, Milo?

   • The galaxy is cooling down
   • The galaxy is moving away
   • The galaxy is moving toward us
8. 7.

   A star is moving toward us. Which way is its light shifted, Noah?

   • Toward red, longer wavelengths
   • Toward blue, shorter wavelengths
   • It isn't shifted, since light is so fast
9. 8.

   Which waves show a Doppler shift, Pia?

   • Sound but not light
   • Light but not sound
   • Both sound and light
10. 9.

    A listener on a moving train passes a horn that stands still beside the track. How does the horn sound while approaching it, Ren?

    • Lower than its own pitch
    • The same, since the horn isn't moving
    • Higher than its own pitch
11. 10.

    After passing the still horn, the listener's train moves away from it. How does the horn sound now, Tala?

    • Lower than its own pitch
    • Silent
    • Higher than its own pitch