Question

Mattias stands in front of a cliff. He shouts "Hello". After 0.4 s here he echoes.

 How far from the cliff is Mattias? Round to ten meters.

Answer 1

Assume that the speed of sound is 340 m/s. The distance between the cliff and Mattias is

$$d=v·\dfrac t2=340·\dfrac{0.4}{2}=68\text{ m}.$$