StudyBrixFree worksheets, study guides and courses

Physics · Grades 8–11

Sound, echoes and travel time

Use round-trip reasoning and distinguish medium effects from source pitch.

Make a worksheet

Learn the idea

Sound as a wave

Sound in air is a mechanical longitudinal wave in the basic model; compressions and rarefactions move through the medium.

Echo

An echo's travel time includes the outward and return path, so a single-reflector distance is vt/2.

Frequency

Pitch is associated with frequency. Medium and conditions influence sound speed.

Model limits

Use the sound speed supplied in the problem. Do not assume one value applies to every material and temperature.

Worked examples

An echo returns in 0.6 s with sound speed 340 m/s. Find distance to the reflector.

The round-trip length is 204 m; divide by two.

102 m

Why is an echo distance often divided by two?

The measured duration is for a round trip.

The sound travels to the reflector and back.

Check your understanding

  1. Which change generally corresponds to a higher pitch from a stationary source?

    1. Higher frequency
    2. Only greater amplitude
    3. Longer period

  2. Sound travels 680 m at 340 m/s. Find travel time.

  3. Why should a water echo problem not automatically use a sound speed for air?

Answers and marking notes

Answers and marking notes
  1. Higher frequency

    Pitch is associated with frequency, not amplitude alone.

  2. 2 s

    t = d/v = 680/340 = 2 s.

  3. Propagation speed depends on the medium and its conditions.

    Credit the supplied medium-specific value.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.