Sound waves travel at the rate of 343 m/s at 20°C. If a man standing 450 meters away from the wall of a canyon yells, “Hello,” how long will it take for him to hear his own voice echo off of the wall?

2.62seconds

Explanation:

Echo occurs when sound reflects and causing a delay before getting to the listener.

Let x be the distance from between the source and the reflector

t be the time taken for the echo to occur

v be the velocity of sound in air.

Using the relationship 2x = vt

t = 2x/v

Given x = 450metres

v = 343m/s

t = 2(450)/343

t = 900/343

t = 2.62seconds

It will take 2.62 seconds for him to hear his own voice echo off of the wall.