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Physics · Grades 8–11

Distance from an echo

The recorded time includes travel to the reflector and back.

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Rule and assumptions

The recorded time includes travel to the reflector and back.

d = vt/2

Worked examples

An echo returns after 740 ms. The sound speed in this medium is 330 m/s. Find the distance to the stationary reflector. Round to 3 decimal places if needed. Answer in m.

d = vt/2 330 × (740/1000) / 2 = 122.1

122.1 m

An echo returns after 1050 ms. The sound speed in this medium is 330 m/s. Find the distance to the stationary reflector. Round to 3 decimal places if needed. Answer in m.

d = vt/2 330 × (1050/1000) / 2 = 173.25

173.25 m

Try two questions

  1. An echo returns after 1120 ms. The sound speed in this medium is 340 m/s. Find the distance to the stationary reflector. Round to 3 decimal places if needed. Answer in m.

  2. An echo returns after 1630 ms. The sound speed in this medium is 330 m/s. Find the distance to the stationary reflector. Round to 3 decimal places if needed. Answer in m.

Answers and reasoning

Answers and marking notes
  1. 190.4 m

    d = vt/2 340 × (1120/1000) / 2 = 190.4

  2. 268.95 m

    d = vt/2 330 × (1630/1000) / 2 = 268.95

Further reading and review references

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

Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.