A herdsman yelling out to fellow herdsman heard his voice reflected by a cliff 4s later. What is the velocity of sound in air if the cliff is 680m away

Jamb 1978

A herdsman yelling out to fellow herdsman heard his voice reflected by a cliff 4s later. What is the velocity of sound in air if the cliff is 680m away? A. 170m/s B. 136m/s C. 340m/s D. 680m/s E. 510m/s

ANSWER: Option C

EXPLANATION: Apply the formula below;

V = 2d/t

Why 2d? Because for an observer to hear an echo, it means the sound travels a distance, hits an obstacle and then reflects back the same distance from the observer! Meaning, it travels twice the distance between the observer and the obstacle!

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