an observer hears an echo 1.26 seconds after blowing a whistle near a cliff. calculate the distance of the…

Analyze the question

The sound travels from the observer to the cliff and back again. The echo time of 1.26 s therefore covers twice the distance between the observer and the cliff.

Concept

Speed = distance ÷ time, so total distance = speed × time.

For an echo: 2d = v × t d = (v × t) / 2

Solution

• v = 330 m/s
• t = 1.26 s

2d = 330 × 1.26 = 415.8 m

d = 415.8 / 2 = 207.9 m

Answer

The observer is 207.9 m from the cliff.

Tip

Whenever you see "echo", divide by 2. Option C (415.8 m) is the trap answer: it is the total distance travelled by the sound, not the distance to the cliff. Always ask yourself, "Is this the one-way distance or the round trip?"