Pickles AcademyStart for free

Speed of sound and echoes – practice for Years 8–9

Sample questions on Speed of sound and echoes with the right answer and a worked solution, from easy to hard. In the Pickles Academy app a child gets new questions of the same kind every time, so they can't just learn the answers by heart.

Subject
Physics
Year
Years 8–9
Curriculum area
Sound

Question types: Speed of sound and echoes

Rule: Speed of sound and echoes

Sound travels at about 340 m/s in air and about 1500 m/s in water. It can’t travel through a vacuum.

An echo goes to the obstacle and back: distance = speed × time ÷ 2.

Example: An echo after 2 s: 340 × 2 ÷ 2 = 340 m

Watch out: Don’t forget to divide by two: the sound travels there and back.

Sample questions

  1. Question 1 Easy

    We heard the thunder 5 s after the flash of lightning. How far away did the lightning strike (in metres)? The speed of sound in air is 340 m/s.

    Show the solution
    Answer: 1700 m

    How it works: The light reaches us almost at once; s = v × t = 340 m/s × 5 s = 1700 m.

  2. Question 2 Normal

    We clapped in front of a cliff and heard the echo after 1.5 s. How far away is the cliff? The speed of sound in air is 340 m/s.

    Show the solution
    Answer: 255 m

    How it works: The sound goes to the cliff and back: 340 m/s × 1.5 s = 510 m, half of that is 255 m.

  3. Question 3 Hard

    A ship’s sonar sends a sound pulse to the sea bed and picks up the echo after 1 s. How deep is the sea? The speed of sound in water is 1500 m/s.

    Show the solution
    Answer: 750 m

    How it works: 1500 m/s × 1 s = 1500 m there and back; 1500 ÷ 2 = 750 m.

Related topics

All Physics topics

Keep practising in the app

In a minute, your child has their own avatar and a first task. Free, no ads, data in the EU.

Start for free